The American Federation of Government Employees (AFGE) has filed a complaint in federal court seeking damages for the nearly 400,000 federal employees who are working without pay during the shutdown.

Politico:

The two plaintiffs — Justin Tarovisky and Grayson Sharp — work for high-security prisons the Justice Department runs. The American Federation of Government Employees argues that both plaintiffs have dangerous jobs and have been forced to work overtime without pay.

AFGE represents roughly 700,000 federal employees and has challenged the Trump administration over a number of issues, including major restructuring at the Education Department.

J. David Cox, AFGE’s national president, said forcing federal employees 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,” he said in a statement. “They are front-line public safety positions, including many in law enforcement, among other critical roles. Our intent is to force the government and the administration to make all federal employees whole.”

The complaint names "The United States of America" as defendant. But there is only one branch of government responsible for funding the agencies the employees work for and that's the Congress. 

The two plaintiffs in the case work at a high security prison, while other employees forced to stay on the job work for the border patrol, immigration enforcement, and airline security. 

While you can certainly sympathize with the federal workers who are forced to stay on the job, no one held a gun to their head when they applied for the job. Is it "fair" that they find themselves in this situation? I guess a federal judge will determine that.

There was a shutdown in 2013 and the case is still tied up in federal court. Recently, a judge ruled that employees are entitled to double the back pay they are owed. It's not clear if the government will appeal that ruling.