Amid the ongoing shutdown brought on by President Donald Trump's refusal to pass funding measures without $5 billion for his "border wall," the nation's largest union of federal workers sued the Trump administration on Monday for forcing them to work without pay doing some of the most essential—and in many cases the most dangerous—jobs performed by government employees.

J. David Cox Sr., national president of American Federation of Government Employees (AFGE), said the lawsuit was necessary to protect workers' livelihoods—and their very lives.

"Our members put their lives on the line to keep our country safe," said Cox, "requiring them to work without pay is nothing short of inhumane. Positions that are considered 'essential' during a government shutdown are some of the most dangerous jobs in the federal government."

Closing out the year strong with our newest lawsuit (filed moments ago) against the government. We’re working nonstop to make sure 2019 is a better year for government employees! https://t.co/FdQAFmKXfa — AFGE (@AFGENational) December 31, 2018

Cox explained that many workers forced to work without pay are frontline public safety positions, including many in law enforcement and others serving critical public safety roles.

"The harm to federal employees began at the first moment of the shutdown," said Heidi Burakiewicz, partner at KCNF DC, the law firm representing AFGE's members in the suit. "Hundreds of thousands of federal employees are working under sometimes dangerous conditions, including the plaintiffs who were forced to work overtime without pay."

A statement put out by the AFGE and its lawyers explained that the lawsuit (pdf) was brought on behalf of all "essential" federal employees, those who are required to work without pay during the shutdown. The Bureau of Prisons (BOP), and the high security penitentiaries where the named plaintiffs work, specifically USP Hazelton and USP Canaan, the statement explained, are "egregiously understaffed" and often require employees to work large amounts of overtime in some of the most dangerous prisons in the country.

According to Burakiewicz, the forced work by federal employees is a "blatant violation" of the Fair Labor Standards Act. "Approximately 420,000 federal employees are continuing to work, but don't know when they will get their next paychecks," she said. "This is not an acceptable way for any employer, let alone the U.S. government, to treat its employees. These employees still need to pay childcare expenses, buy gas, and incur other expenses to go to work every day and yet, they are not getting paid."