Meanwhile, Donald Trump has backed away from the prospect of declaring a national emergency
A partial US government shutdown has now become the longest on record.
Yesterday, around 800,000 federal workers didn't receive their wages for the first time since the shutdown began in December.
The dispute revolves around Donald Trump's demand for more than $5 billion to build a US-Mexico border wall.
Democrats have refused to fund the wall - although bipartisan efforts to reopen the government have included extra money for border security.
The political impasse means that necessary legislation to fund several federal agencies and services has not been passed - leading to a funding gap.
Hundreds of thousands of workers - ranging from air traffic controllers to museum staff - have been forced to work without pay, while others have been sent home on unpaid leave (furlough).
As well as workers going unpaid, there have been numerous other consequences - many museums and galleries in Washington DC remain closed, while national parks around the country have been understaffed with widespread reports of rubbish going uncollected and toilets overflowing.
With the shutdown entering its fourth week today, the 22-day political crisis has officially surpassed the previous record.
That occurred in 1995-96, amid funding disagreements between the Republican-controlled Congress and President Bill Clinton.
No apparent progress has been made to end the current shutdown, with Donald Trump having this week suddenly walked out of a White House meeting with Democratic leaders after House speaker Nancy Pelosi repeated that they wouldn't fund the wall.
The US President has previously hinted he could use executive powers to declare a national emergency and divert military funding in order to build a wall.
However, he yesterday backed away from that proposal, citing the expectation that such a move would provoke swift legal challenges.
Speaking at the White House, President Trump said: "What we're not looking to do right now is national emergency.
"It's the easy way out. Congress should do this. This is too simple. It's too basic. And Congress should do this."
Meanwhile, Senator Lindsey Graham - a Trump ally in the Senate - demanded that the President declare a national emergency:
Mr. President,— Lindsey Graham (@LindseyGrahamSC) January 11, 2019
Declare a national emergency NOW.
Build a wall NOW.
While Republican leadership has stuck firmly by Trump's stance so far, a small number of the party's moderate senators - some of whom face tough re-election battles next year - earlier this week suggested the government should be reopened and border security be dealt with separately.