When a New Mexico immigration detention facility needed people to cook for inmates and clean its halls, it found a solution already inside its walls.

For $0.50 or less per hour, detainees such as Mbah Emmanuel Abi and Desmond Ndambi, who have since been granted political asylum, cooked meals for their fellow inmates and worked in the facility library.

Their experience is not unique: for $1 a day – and sometimes less – migrants prepare meals, clean facilities and do laundry at privately run immigration detention centers across the country.

The practice has been compared to slave labor and has brought a pile of lawsuits to the doorsteps of the country’s two biggest private prison companies, CoreCivic and Geo Group, which in 2017 had a combined $4bn in revenue.

In a recently filed class-action lawsuit, Abi, Ndambi and one other man who fled Cameroon in 2017, brought wage theft claims against CoreCivic’s Cibola county correctional center in New Mexico.

“The fact that the company is able to obtain the labor it needs to function, for the facility to function, at vastly below market rates is part of its business model,” Joseph Sellers, an attorney at Cohen Milstein who is representing the plaintiffs, told the Guardian.

Both CoreCivic and Geo Group have said the pay is compliant with a voluntary work program mandated by the government, but attorneys said the labor is not voluntary because it is needed to pay for items such as toothpaste or to make phone calls to loved ones.

“I wouldn’t call it voluntarily,” Sellers said. “They do this work because they need the income, which is meager, certainly, to help pay for sundries and various things like toothpaste they may need while they are confined and don’t otherwise have.”

The New Mexico case was filed in a federal court in Maryland last week and centers on CoreCivic’s alleged violation of minimum wage laws.

“We’re looking into it in other places,” Sellers said. “It regrettably appears to be a widespread phenomenon.”

In the past four years, other ongoing lawsuits about $1-a-day pay have accused private prison companies of also violating laws that prohibit forced labor and unjust enrichment.

In April, a class-action lawsuit was filed against CoreCivic for using “forced labor” at a facility in Georgia. A plaintiff from Guatemala, Wilhen Hill Barrientos, said he had to work to pay for phone calls to his family, who he couldn’t speak to without doing work for about $0.50 per hour.

In September 2017, Washington state filed suit against Geo Group for paying detainees $1 a day.

Detainees at an Aurora, Colorado, facility sued Geo Group for wage theft in 2014. This case, like the others, is still working through the courts.

Amanda Gilchrist, a Core-Civic spokeswoman, said the company could not comment on pending litigation, but saidits work programs were “completely voluntary and operated in full compliance with Ice standards”.

“We set and deliver the same high standard of care – including three daily meals, access to health care and other everyday living needs – regardless of whether a detainee participates in a voluntary work program,” Gilchrist said in an email.

Pablo Paez, a Geo Group spokesman, also said in a statement that the company complied with national, government-established standards for voluntary work.

“The wage rates associated with this federally-mandated program are stipulated under long-established guidelines set by the United States Congress,” Paez said. “As a service provider to the federal government, Geo is required to abide by these federally mandated standards and congressionally established guidelines.”

Both companies contributed to Trump’s presidential campaign and have benefited from his administration’s harsh immigration policies, which include reversing Obama administration efforts to reduce the federal government’s use of private prisons.

The day after the 2016 presidential election, Geo Group’s stock prices increased 21% and CoreCivic’s increased 43%. In earnings calls, company leaders have predicted increased profits because of the increasing immigration arrests in the US.

The founding director of Northwestern University’s Deportation Research Clinic, Jacqueline Stevens, prompted the 2014 Colorado lawsuit through her research of private prisons’ voluntary work schemes.

Stevens said these extraordinarily low pay rates also impact local wages and other industries.

“The purpose of these laws isn’t simply to protect the earning rights of the people who are being exploited, but also the average wages of people in a particular community,” Stevens said. “That’s why there are all sorts of rules and precedents that say that if employers hire people below that, even if it looks like someone is consenting, it is still unlawful.”

She said many strands of US laws prevent companies from compelling people who haven’t been convicted of crimes to work; define volunteers as doing work for no pay for humanitarian purposes and protect local wages by prohibiting companies from paying people less than an agreed-to standard.

Stevens said: “When you are able to hire people for a $1 a day or less, you undercut the employment opportunities for everybody else.”