America’s foreign aid agency could see its staff slashed from about 10,000 to fewer than 300 globally as the Trump administration makes major cuts to government spending.

All but a handful of essential staff are already set to be placed on administrative leave at midnight on Friday, including thousands based abroad. An online notice says a plan is being prepared for return travel and the termination of non-essential contractors.

One union representing employees – which is involved in a legal challenge to the plan – told the BBC’s US partner CBS News that just 294 staff have been deemed essential.

Trump’s cutbacks to USAID – championed by his cost-cutting advisor Elon Musk – have upended the global aid system, with hundreds of programmes already frozen in countries around the world.

His team accuses USAID of wasting taxpayer money and failing to align with “America First” policy priorities.

Polling has indicated scepticism among many Americans for foreign aid. An AP-NORC poll from March 2023 suggested as many as nine in 10 Republicans felt the country was overspending.

The move is just one example of Trump’s efforts to slash federal spending since returning to the White House. He campaigned on overhauling the federal government and formed an advisory body named the Department of Government Efficiency (Doge) – led by Musk – to cut the federal budget.

The US is by far the biggest single provider of humanitarian aid around the world. It has bases in more than 60 countries and works in dozens of others, with much of its work carried out by its contractors.

Former USAID chiefs have criticised the reported cutback plan. One of them, Gayle Smith, stressed to the BBC World Service’s Newsday programme that the US had always been the fastest to arrive during humanitarian crises around the world.

“When you pull all of that out, you send some very dangerous messages,” Smith said. “The US is signalling that we don’t frankly care whether people live or die and that we’re not a reliable partner.”

The suggestion that only 294 staff were on the “essential” list was made by the American Foreign Service Association union (AFSA). It has teamed up with another labour group, the American Federation of Government Employees (AFGE), to file a lawsuit challenging the plan.

As well as the president, the lawsuit takes aim at the US state department, USAID, the treasury department, the secretary of state and Treasury Secretary Scott Bessent.

The lawsuit argues that the president is violating the US Constitution and federal law by attempting to dismantle the agency. “Not a single one of defendants’ actions to dismantle USAID were taken pursuant to congressional authorization,” it says.

“And pursuant to federal statute, Congress is the only entity that may lawfully dismantle the agency.”

It calls for an independent acting director of USAID to be appointed, for USAID buildings to be reopened to employees, for the USAID website to be restored, for grants and contracts to be reinstated, and for mandatory evacuation notices to staff to be lifted.

It asks for a judge to immediately halt the implementation of the plan to “gut” USAID, which the lawsuit notes has been spearheaded by Elon Musk, due to the urgent need to resume to aid programmes.

“These actions have generated a global humanitarian crisis by abruptly halting the crucial work of USAID employees, grantees, and contractors. They have cost thousands of American jobs. And they have imperilled US national security interests,” the lawsuit says.

Thousands of USAID workers expect to be put on administrative leave from Friday night. A message posted on the agency’s website says this will apply to all direct hire personnel from 23:59 EST (04:59 GMT).

Congressman Raja Krishnamoorthi, a Democrat from Illinois, told the BBC the cuts were “horrible news for global public health”.

“There are ways to reform the USAID in a fashion that is much less harmful to the mission of the agency and to all the beneficiaries than the way in which it’s being conducted right now,” he said.

As the turmoil continues to be felt around the world, one leader of a non-government organisation (NGO) tackling HIV in Kenya – which is partly funded by USAID – described the impacts.

Nelson Otwoma told the BBC World Service that his NGO had been affected “adversely” by the freeze, describing massive job layoffs of individuals supported by USAID and the Centers for Disease Control and Prevention (CDC).

This has led to fear and anxiety as people are not getting their medicine in facilities supported by USAID where layoffs occurred, he said. “We don’t know what tomorrow brings… things have ground to a halt.”

Earlier this week, reports suggested that the Trump administration planned to merge USAID with the state department. Secretary of State Marco Rubio said he had become USAID’s acting head.

He has defended Trump’s moves, telling about 200 agency workers in Guatemala on Wednesday that the US did not plan to stop distributing aid to foreign countries. But he said that the programmes must align with US priorities.

“The United States is not walking away from foreign aid,” America’s top diplomat said. “It’s not. We’re going to continue to provide foreign aid and to be involved in programmes, but it has to be programmes that we can defend.”

“It has to be programmes that we can explain. It has to be programmes that we can justify. Otherwise, we do endanger foreign aid.”