Photo taken on Dec. 28, 2018 shows the reflection of the Capitol Hill on an ambulance's door in Washington D.C., the United States. The U.S. Senate convened briefly Thursday afternoon before adjourning until next week, with no signs of a deal to end the budget impasse that has shut down a quarter of the federal government. The upper chamber will convene on Monday, Dec. 31, for a pro forma session only, and then return to the Capitol Hill to renew budget deliberations on Wednesday, Jan. 2, a day before Democrats are set to take control of the House. (Xinhua/Liu Jie)

WASHINGTON, Dec. 31 (Xinhua) -- A federal employee union sued the Trump administration on Monday over the ongoing partial government shutdown, claiming that it is illegal for agencies to force employees to work without pay.

The lawsuit was filed by the American Federation of Government Employees (AFGE) as the partial shutdown is dragging into the new year. Hundreds of thousands of workers have been furloughed or are working without pay during the shutdown.

"Our members put their lives on the line to keep our country safe," said J. David Cox Sr., the union's national president. "Requiring them to work without pay is nothing short of inhumane."

The AFGE, one of the largest federal employee unions, sued the federal government on similar grounds following a 16-day shutdown in 2013.

This partial shutdown began on Dec. 22 after the White House and Congress disagreed over whether to provide billions of U.S. dollars for the construction of a U.S.-Mexico border wall promised by Trump during his 2016 presidential campaign.

Trump and his conservative allies have insisted that the border wall is essential to addressing illegal immigration and drug trafficking, while Democrats have slammed the proposal as an "inefficient, unnecessary and costly" solution to strengthening border security.

Both sides have tried to pin blame on the other since the shutdown. Meanwhile, there has been little contact between the White House and congressional Democrats for more than a week.

House Democrats unveiled a package of bills on Monday that would end the partial shutdown, but deny funding for Trump's border wall, setting the stage for renewed confrontations between the White House and Congress.

The lower chamber is reportedly preparing to vote as soon as the new Congress convenes Thursday when Democrats take over the House.

Trump told Fox News Channel in an interview aired Monday night that he was "ready, willing and able" to negotiate while suggesting that he has not given up on the border wall.

"We are not giving up," the president said in the year-end interview. "We have to have border security and the wall is a big part of border security."