WASHINGTON, Jan. 11 (Xinhua) -- The U.S. National Air Traffic Controllers Association (NATCA) on Friday sued the federal government as its members are working without pay during the ongoing partial government shutdown.

The lawsuit, filed in the federal court in Washington D.C., claimed that the government is in violation of the Fifth Amendment of the U.S. Constitution, because it "unlawfully deprived NATCA members of their earned wages without due process," according to a press release.

The association accused the government of violating the Fair Labor Standards Act because it is not paying air traffic controllers at least minimum wage and because the Federal Aviation Administration (FAA) did not pay them overtime during the shutdown, TheHill news daily said.

"On behalf of its members, NATCA seeks an order requiring the government to pay its members for the work they have performed as well as liquidated damages," the release said.

The lawsuit comes as the shutdown stretched into the 21st day on Friday, tying the record for the longest in the country's history.

U.S. President Donald Trump has locked himself in a stalemate with congressional Democrats in the dispute over his demand for 5.7 billion U.S. dollars for funding a wall along the U.S.-Mexico border.

The partisan fight, with no end in sight, is about to make the partial government shutdown the longest in U.S. history on Saturday.

About 800,000 federal workers, who have been forced to go on unpaid leave or work without pay since Dec. 22 when the shutdown started, will have to miss a paycheck on Friday, which was supposed to be payday.

The NATCA represents some 19,000 FAA employees, which includes 14,000 air traffic controllers.