A union representing 150,000 executive branch employees sued the federal government Jan. 9, asking a court to declare unconstitutional the section of the Antideficiency Act that requires certain employees to work without pay indefinitely.

Congress holds the power of the purse, so the Antideficiency Act “is unconstitutional insofar as it purports to authorize the executive branch to obligate funds that have not been appropriated,” the National Treasury Employees Union said in its complaint.

The NTEU is the exclusive bargaining representative for employees in 32 federal departments and agencies, according to its complaint.

Further, only workers whose job duties are tied...