Five anonymous federal workers are suing President Donald Trump over the ongoing partial government shutdown, saying that being forced to work without pay amounts to unconstitutional involuntary servitude.

The lawsuit was filed this week in the U.S. District Court for the District of Columbia and is one of a growing number of legal attempts to end the 20-day-old shutdown. Two unions representing federal workers have already sued the Trump administration over the shutdown, which has affected some 800,000 federal workers — though roughly half of those have been deemed “essential” and are working without pay.

The five employees work at four federal agencies: the Department of Justice, the Department of Transportation, the Department of Agriculture and the Department of Homeland Security. Four of them are working without pay, and they say that amounts to involuntary servitude, a violation of the 13th Amendment. The remaining worker has been furloughed, and says that restrictions on his ability to look for another job during the shutdown violates the Fifth Amendment.

The lawsuit also says the government too broadly declared certain employees “essential” and required them to report for work, without specifically showing that their duties reach the threshold for that designation. One of the employees is an air traffic control specialist who says she is not tasked with “duties related to the protection of human life or property” and should not have been required to work without pay.

“They’re not getting paid, they’ve got bills to pay, and they’re foreclosed from making any income to meet their obligations,” said Michael Kator, the attorney representing the five government workers. “That’s what this lawsuit is about: finding a way for our plaintiffs to satisfy their obligations to live their lives while this fight goes on.”

The lawsuit asks a federal judge to prohibit the government from forcing employees to report to work during the shutdown or taking any action against employees who don’t show up. It also asks the judge to order that federal workers be allowed to seek outside employment during the shutdown. The five workers involved in the suit are currently precluded from doing so.

The partial shutdown started on Dec. 22, but the federal workers who have been impacted are expected to feel a hit this week, when many will miss their first paycheck. Roughly 5,000 federal employees in the Washington region have filed for unemployment benefits, according to a report from The Huffington Post.

If the shutdown continues through Saturday, it will become the longest in U.S. history.