Thousands gathered at the US Capitol on Wednesday after the shock announcement on Tuesday evening that the US Agency for International Development (USAid) was putting nearly all of its employees on leave and recalling thousands of officers from their postings abroad.

The news came only days after nearly a thousand contractors were laid off or furloughed, the USAid website was taken down, and its X account was deleted.

Protesters gathered near the Capitol under chilly, overcast skies and chanted: “Let us work!” and “USAid! USAid!”

“We are in a very, very dire place,” Jeremy Konyndyk, a top USAid health official under Barack Obama and Joe Biden, told the crowd. “The attempt to kill USAid will kill people.”

Competitors such as Russia and China were cheering this decision, he added.

His voice rose as he addressed members of Congress in the halls behind him – especially lawmakers, he said, who had supported the agency and its work for years.

“You know that what is being said about USAid is not true,” Konyndyk said. “Speak up! Where are you?”

“This is a dictatorship in the making,” Ed Markey, a senator from Massachusetts, told the crowd. “This is an example” of what the Trump administration can do to agencies such as the US Environmental Protection Agency (EPA), he said.

“We are the moral force of the world,” Markey said. “The only way to take back our government is to take to the streets by the millions to demand justice, not just for our country but for people around the world.”

Nearly all of USAid’s work, which includes preventing HIV and famine as well as rebuilding nations after conflict and improving education, was halted unexpectedly on 24 January for a 90-day review.

Experts say the erasure of the agency is a test run for the Trump administration, which has also put agencies such as the Department of Education and the National Oceanic and Atmospheric Administration (Noaa) in its crosshairs.

“This is showing that you can do a slash-and-burn to the American governmental apparatus, including foreign aid,” Joia Mukherjee, chief medical officer of the non-profit Partners in Health, told the Guardian.

While USAid has enjoyed bipartisan support in the past, it’s now a target for conservatives. But Mukherjee said that nothing about aid work had changed in Washington.

“I think the fidelity to Trump changed,” she said. Members of Congress are “afraid of Trump”, she added. “This is just a loyalty test.”

Pete Marocco, who was allegedly photographed and filmed at the January 6 riots, appeared to threaten aid workers with military action if they didn’t comply with evacuation orders, according to a source at USAid who read the recall letter.

Marocco was named deputy administrator of USAid on Monday by the secretary of state, Marco Rubio. That position needs confirmation by the US Senate before being filled.

Rubio seized control of the agency to fold it into the state department after alleging that officials at the agency had been too “independent”, Rubio told reporters on Monday.

The aid agency was founded in 1961, but was enshrined into law as an independent agency by Congress in 1998. Only lawmakers have the power to dismantle or move it.

“What’s happening is unconstitutional and illegal,” said Sharon Baker, who worked on grants and contracts for USAid for 11 years before retiring.

“It’s enormous – it affects all Americans,” she said, before adding of USAid staff: “In global emergencies, they’re the first responders. [After earthquakes and tsunamis], they’re the ones who are there first. You see airplanes offloading supplies that say ‘from the American people’.”

The move to stop work and dissolve the agency into the state department without direction from Congress is unprecedented, said one contractor who worked for USAid for 20 years before being furloughed last week.

“It puts us and the world in danger in a way it never has before,” said the contractor, who requested anonymity to protect their job.

“I think this is Project 2025 in action. They’re doing what they said they would do.”

The stop-work order is “the most catastrophic thing we’ve seen in foreign aid since we started working on famine in Ethiopia in the 80s”, said Crickett Nicovich, who works for the non-profit Results.

“Congress needs to stand up and defend USAid. Conservatives have told us that they care about these issues for years,” Nicovich said.

“Without them pushing back, this dismantling of programs is costing hundreds of thousands of lives around the world.”