Monday's lockout added to the chaos that has consumed the agency, which distributes billions of dollars of humanitarian aid around the world, since Trump ordered a freeze on most US foreign aid hours after taking office on January 20.
USAID has been targeted for closure by billionaire Elon Musk, who has been tasked by the president with downsizing the federal government.Â
A senior White House official, speaking on condition of anonymity, said Trump was considering merging USAID into the State Department and had "entrusted Elon to oversee the efficiency of this agency."
A group of Democratic lawmakers, cheered by dozens of furloughed agency employees and contractors, held a protest in front of the USAID headquarters, which was shut to the employees on Monday, according to an internal email seen by Reuters.
USAID staff were blocked from entering agency's headquarters in Washington. (EPA PHOTO)
Another internal email seen by Reuters went out late on Monday, telling employees at the agency's headquarters and a second site in Washington to work remotely again on Tuesday, adding to concerns voiced by staff members and lawmakers.
"We don't have a fourth branch of government called Elon Musk," said US Representative Jamie Raskin, speaking outside the building.
Senators Brian Schatz and Chris Van Hollen said they would block confirmation of Trump's nominees for State Department positions under rules that allow them to hold up nominations even if the Republican majority of the chamber want them to move forward.
"We have control over the calendar for nominees," said Van Hollen. "We will do everything we can to block State Department nominees from going forward until this illegal action is reversed."
Hundreds of USAID programs covering billions of dollars worth of lifesaving aid across the globe came to a grinding halt after Trump on January 20 ordered a freeze of most US foreign aid, saying he wanted to ensure it is aligned with his "America First" policy.
If USAID were put under the State Department, it would likely have dramatic consequences for the distribution of aid from the United States, the world's largest single donor.
Musk has been increasingly critical of USAID, calling it a left-wing agency unaccountable to the White House that is "beyond repair". Musk critics say his accusations are often lodged without evidence and may be ideologically driven.
Democrats have argued that eliminating USAID's independence requires an act of Congress. Trump told reporters on Monday that he did not believe that was necessary.
"I love the concept (of USAID), but they turned out to be radical left lunatics," Trump said.
US Secretary of State Marco Rubio told reporters in San Salvador that he was now the acting head of USAID, calling the agency "completely unresponsive" and accusing the staff there of being "unwilling to answer simple questions" about programs.
He informed Congress in a letter of the looming reorganisation of the agency, saying some parts of USAID might be absorbed by the State Department and the remainder may be abolished.
