A company owned by two of Donald Trump’s top mega-donors has routinely brought dozens of its workers from Mexico to staff its warehouses in Wisconsin and other locations even though they do not appear to have permission to work in the US, according to a Guardian investigation.

Uline – a giant Wisconsin-based office and shipping supply company controlled by billionaires Liz and Dick Uihlein – shuttles in its own workers from Mexico, who are using tourist visas and visas meant for employees who are entering the US temporarily to receive professional training, known as B1 visas. But instead of being part of a dedicated training program, the Mexican employees stay for one to six months and – sources with direct knowledge of the matter allege – perform normal work in Uline’s US warehouses.

Lawyers and immigrants’ advocates told the Guardian they believed the alleged practice is likely illegal and could be exploitative of the workers enrolled in the program.

The company has allegedly used employees without proper work permits even as Dick Uihlein’s Super Pac, Restoration Pac, supported Trump’s presidential campaign with a TV advertisement attacking his opponent Kamala Harris for allowing an immigrant “invasion” at the US-Mexico border. The Uihleins have emerged as a major force in rightwing politics, spending tens of millions of dollars supporting candidates, including president-elect Trump and other rightwing politicians, who have called for a mass deportation of immigrants. They were the second-largest political donors in this year’s election, giving more than even Elon Musk, the world’s richest man.

Inside Uline, a privately held company worth an estimated $8bn, the Mexico-US program is called “shuttle support” and was launched about three years ago, sources said.

The Guardian’s reporting is based on interviews with sources who have direct knowledge of shuttle support and spoke on the condition of anonymity because of fear of reprisals, and internal documents seen by the Guardian that referred to the worker program, including rules for family members and other guests who are allowed to visit the workers. Over the course of a months-long investigation, Guardian reporters also observed a dozen Uline workers from Mexico living in a hotel near the company’s Pleasant Prairie headquarters, where the company pays for their lodging, food and rental cars. A staff member at the hotel confirmed that Uline was among the first customers at the hotel to book “blocks” of suites for workers when the hotel opened about three years ago.

A spokesperson for Uline and the Uihleins declined to comment.

Sources who spoke to the Guardian alleged that executives at the highest level of the company, including Liz Uihlein, know about shuttle support. It is not clear why executives have turned to staff that are employed by Uline in Mexico to work at their US warehouses, but sources said it could be connected to the company’s strict and complicated hiring practices, which include follicle drug testing of employees.

“They were not able to staff their warehouses, especially in Pennsylvania. So they looked at Mexico for workforce,” alleged one person with close knowledge of the matter.

The Mexican workers have an implicit understanding that they should tell border officials that they are entering the US to be trained at Uline, sources alleged.

One Uline document seen by the Guardian, which was used by a Uline employee in Mexico to enter the US, said the employee would be receiving training in warehouse safety, understanding how to use vehicle-mounted unit devices, and understanding how to identify warehouse locations. Legal experts said B1 visas are intended to be used for short-term visits – no longer than six months – and that workers are not meant to engage in “productive employment” in that time.

Once the Mexican workers enter the US, sources alleged, they work regular shifts in Uline warehouses alongside their American counterparts.

“They are actually doing work. Not training,” said one person with direct knowledge of the situation. The person added that Uline was “very careful” with the amount of time the Mexican employees stayed in the US.

They are paid their Mexican wages into accounts in Mexico. Although they receive some extra compensation for traveling to the US and staying there, they are paid far less than American counterparts, sources told the Guardian.

“The reason employees want to participate is because they give bonuses to those employees. They are risking their [tourist] visas. If they find out they are working, their visas would be revoked,” said one person with direct knowledge of the matter.

The sources who spoke to the Guardian said Uline pays all the costs for their Mexico-based workers to leave Mexico and fly to warehouse locations in the US, including in Wisconsin and Allentown, Pennsylvania. About 60 to 70 workers from the company’s sites in Mexico may be working in the US at any time, the sources alleged.

One internal Uline document reviewed by the Guardian suggests that at least some Uline workers in Mexico have been hired expressly to take part in the shuttle support program, and that workers understand that their future jobs are dependent on their participation in the program for indefinite periods.

Another internal document shows that requests for Mexican participants came from a senior executive at Uline’s Pleasant Prairie headquarters, where some warehouses are based.

3,000 miles from home

The corporate hotel in Wisconsin where at least a dozen Uline workers from Mexico live is about 3,000 miles (4,800km) from their homes in Mexico. Some are accompanied by their wives for their stay. Most participants in the shuttle support program are men.

The hotel is comfortable, and was designed to meet the needs of long-term guests. The clean and modern suites have kitchenettes, and breakfast is served every morning: a waffle machine, granola, eggs and dry cereal, and salsa, cheese and sour cream. Hotel staff seemed to make an effort for the holidays. The lobby area included a 10ft Christmas tree and other decorations – including four knit stockings, hung over a fake fire off to the side.

Still, the hotel, which the Guardian is not identifying to protect the safety of the workers, is located in a relatively remote location in landscape that would be barren but for the presence of huge warehouses – from Uline to Amazon – along the highway. Uline opened the largest warehouse in Wisconsin here earlier this month, a 1.44m sq ft facility that adds on to the company’s 9.6m sq ft footprint in the Kenosha area.

One Uline worker who spoke to the Guardian but did not provide his name said he had traveled to the US for training, but then proceeded to explain how he was working in the US for a longer period and doing the same kind of work he did in Mexico. He expressed a note of skepticism about the idea that such tasks could be described as “training”. He confirmed he had traveled to the US on his own tourist visa as well as a document that fit the description of a B1 visa, meant for business-related travel – but not wage labor.

‘It really shows the cynicism’

Immigration experts – including lawyers and advocates for immigrant rights – said they believed the shuttle support program appeared to break the law.

The B1 visas that are being used by some of the workers to enter the US are intended for workers to train or briefly attend a seminar or conferences, they said.

“It does not allow them to obtain wages for labor in the United States, it absolutely does not,” said Marc Christopher, a Wisconsin-based immigration lawyer. “If they’re doing warehouse work, especially second or third shift, that’s not a close call.” He added that he believed it was “absolutely 100% not allowed”.

Ira Kurzban, another immigration lawyer, said he believed it was “clearly illegal” for the company to be engaged in a pattern of conduct that possibly involved labor trafficking of people who were coming under “one pretense, but actually coming in for another reason”.

Uline’s alleged use of its Mexican workers to staff warehouses in the US underscored the real difficulties facing some companies, Kurzban said, in being able to secure legal arrangements for workers.

“This is the whole false premise of Trump. I mean, the idea that these people are taking jobs away from Americans. They’re not. We need millions of people to do this kind of work. We’ve always looked away even though we know most people who fulfill these kinds of jobs are not allowed to be working in the US.”

Another immigration lawyer, Mo Goldman from Arizona, said it is a common practice for employers to call him and ask him how to legally employ foreign workers, only to find that the legal processes are “very restrictive and difficult to navigate”.

“It does force employers to look at other ways to get the workers here, because they cannot find the workforce in the United States,” Goldman said.

He added that there have historically been significant civil penalties that have been rendered against companies for doing such things.

Christine Neumann-Ortiz, director of the Wisconsin immigrant and labor rights group Voces de la Frontera, said she believed the program was clearly undermining wages for all workers at the company.

“It is a way for Uline to undercut wages for US workers, while also not paying justly the Mexican workers for what their co-workers are earning here for the exact same work, while also having to sacrifice time away from their families and communities,” Neumann-Ortiz said.

She noted the irony of the Uihleins profiting “off the backs of Mexicans” even as they supported a presidential candidate – and now president-elect – who has vowed to deport immigrants, disparages them and wants to take away birthright citizenship.

“It really shows the cynicism – it’s a model of international labor exploitation, while at the same time really putting money into this propaganda campaign to try to pit workers against each other.”

The anti-immigrant sentiment also contradicts the reality facing American businesses, which is that they are facing severe labor shortages and have depended on the labor of undocumented workers for decades.

“They want to maintain [immigration], but under very oppressed conditions,” she said.

It is not the first time the Uihleins have acted in a way that appears to contradict their rightwing anti-immigration stance. ProPublica reported in 2019 that Uline had sought special visas for foreign workers even as Trump, whom Dick and Liz supported, was implementing his strictest immigration policies. The company even filed suit against the federal government in Illinois after the Trump administration rejected a 2018 petition to hire a full-time software engineer from India. In court testimony in an unrelated case, ProPublica noted, Dick Uihlein, who serves as CEO, was asked if his donations to a group supporting conservative politicians meant he did not just support immigration reform, but a more stringent immigration policy. He said: “I would say that’s correct, yep.”

Election deniers and Maga firebrands

Public records and media reports show the Uihleins became a major force in American politics after the landmark Citizens United decision, which upended campaign finance law and enabled corporations and other special interest groups to spend unlimited sums of money on elections.

Dick and Liz Uihlein have donated millions in support of politicians on the right, including Trump and other election-denying candidates and causes.

The family’s political influence has skyrocketed alongside the growth of their company, which brought in $8bn in revenue in 2024, up from $7bn in 2023 and $6.1bn in 2022. According to Federal Election Commission filings, the Uihleins spent at least $130m during the 2024 election cycle to support Trump and other rightwing Republicans.

Dick Uihlein has, in particular, focused his donations largely on culture-war candidates and Maga firebrands. In 2017, Uihlein was the top funder of Republican Roy Moore’s Senate bid, continuing to run ads in support of Moore even as the Alabama politician faced allegations of sexually assaulting minors. Moore denied any sexual misconduct. In 2022, Dick Uihlein threw his support behind the Pennsylvania gubernatorial candidate Doug Mastriano, a far-right politician who has decried the separation of church and state and peddled conspiracy theories.

In the wake of the January 6 Capitol riots, WBEZ Chicago revealed that Uihlein had bankrolled Tea Party Patriots, a group that helped organize the #StoptheSteal protest that gave way to the insurrectionary violence.

A July investigation by ProPublica and Documented also identified the Uihleins as supporters of Ziklag, a secretive Christian donor network that invested in voter purges, anti-trans activism and pro-Trump electoral infrastructure.

Outside of national politics, Dick Uihlein has demonstrated a particular interest in Wisconsin, where Uline is headquartered, and Illinois politics, where he and his wife live. In 2018, for example, Uihlein poured millions into an Illinois gubernatorial election, supporting the Republican incumbent’s primary challenger with ads blasting LGBTQ+ and abortion rights. During Wisconsin’s 2023 state supreme court race, Restoration Pac and Fair Courts America – groups that Uihlein has bankrolled – spent millions in support of the rightwing candidate Dan Kelly.

One Mexican Uline worker who spoke to the Guardian on the condition of anonymity said he felt the Uihleins’ strong support for Trump was “a little contradictory” given the company’s practice of bringing Mexican workers to the US.

“But I’m here to work, I’m not here in some illegal way,” he added.

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