A partial US government shutdown over President Donald Trump's demand to fund a wall along the US-Mexico border has entered its 22nd day, making it the longest ever in US history.
Trump, holed up in the White House with Congress adjourned for the weekend, has warned of a much lengthier impasse.
"We will be out for a long time unless the Democrats come back from their 'vacations' and get back to work," he tweeted on Saturday.
Democrats say Trump shut the government in a "temper tantrum" by refusing to sign bipartisan funding legislation last year that did not include $US5.7 billion ($A7.9b) for his wall.
The closure, which began on December 22, broke a decades-old record set by a 1995-1996 shutdown under former president Bill Clinton that lasted 21 days.
Roughly 800,000 federal workers who are affected missed their first pay cheques on Friday, heightening concerns about mounting financial pressures on employees.
They include air traffic controllers and airport security officials who continue to work without pay.
Some workers have resorted to selling their possessions or posting appeals on online fundraising sites to help pay their bills.
A union that represents thousands of air traffic controllers sued the Federal Aviation Administration on Friday, saying it had violated federal wage law by failing to pay workers.
It is at least the third lawsuit filed by unions on behalf of unpaid workers.
Trump is considering a possible national emergency declaration that would end the shutdown and allow him to obtain his wall funding by circumventing Congress.
But on Friday, he said he would not take such a step "right now".
"Democrats should come back to Washington and work to end the Shutdown, while at the same time ending the horrible humanitarian crisis at our Southern Border. I am in the White House waiting for you!" he tweeted.
Trump also urged his 57.2 million Twitter followers to contact Democratic lawmakers and "Tell them to get it done!"
Democrats, who call a wall an ineffective, outdated answer to a complex problem, have passed several bills in the House of Representatives to reopen the government without funding for Trump's barrier.
But the legislation has been ignored by the Republican-controlled Senate.
Trump originally pledged Mexico would pay for the wall, which he says is needed to stem the flow of illegal immigrants and drugs.
But Mexico has refused.