Tens of thousands of US government workers have reportedly accepted an offer from the Trump administration to resign in exchange for continued pay until 30 September.

Some two million federal employees were advised they could opt in to the deferred resignation programme - an offer akin to a gradual buy-out - last week.

So far, more than 1% of that workforce has chosen to take part ahead of the Thursday deadline - making up between 20,000 to 40,000 federal workers, according to US media.

The White House, which previously said it expected as many as 200,000 people to accept, told US media they expect a spike in participation in the next 24 hours.

The resignation scheme's announcement - delivered in the form of a late-night email - is part of an ongoing effort by the Trump administration to slash the size of the federal bureaucracy and cut spending.

Unions who represent US government workers have sued to block the plan for mass resignations.

"We won't stand by and let our members become the victims of this con," said American Federation of Government Employees (AFGE) president Everett Kelley in a statement on Tuesday afternoon.

On Tuesday, the Central Intelligence Agency (CIA) became the first national security arm to extend the offer to its staff, telling its entire workforce they could quit and receive about eight months of pay and benefits.

But it was not immediately clear who could accept the offer. Some areas of expertise may be restricted, CNN reported, citing a source familiar.

Newly appointed CIA director John Ratcliffe personally decided he wanted the spy agency to be involved in the resignation programme, the source told CNN.

The CIA is also freezing the hire of those already given a conditional offer, the Wall Street Journal reported, citing an aide to Ratcliffe.

Some of the offers are likely to be rescinded if the applicants do not suit the administration's new priorities, the aide reportedly said, including President Donald Trump's tariffs and working to undermine China.

An analysis of the federal workforce by the non-profit Partnership for Public Service found that the annual attrition rate among federal employees is about 6%, meaning some of those who accept a buy-out offer may have been planning to leave government anyway.

Those who oppose the resignation scheme include AFGE, the largest federal employee union.

In a complaint, it wrote that the proposed buy-outs were "arbitrary and capricious" and violate federal law.

And, the AFGE claims, employees can't rely on the government to deliver on their promise of pay until September. To take part in the buy-out, employees must waive their right to legally challenge their employer in court, according to a Tuesday statement from the government's human resources agency, meaning they must trust that the deal will be honoured.

AFGE also pointed out that the budget currently funding the federal government will expire in March, raising further questions about if eight months of pay could be guaranteed.

But it remains unclear how many people will take up the offer. According to CNN, the Trump administration is planning to implement widespread layoffs for employees who decline it, leaving further uncertainty for those who remain.

Federal employees who spoke to the BBC described an atmosphere of confusion and anxiety, as they weighed what comes next.

One woman who spoke on the condition of anonymity said she had been a federal employee for more than two decades.

"It appears rude and appalling," she said, adding the offer itself seemed "threatening, e.g. 'take it or leave it or your job might be eliminated anyway'".

And there is "no guarantee" for the buy-out programme, she added.

Even workers who said they would take the offer expressed similar concerns: that they may not get the pay they have been promised.

Another federal worker said while he planned on taking the offer, he was not confident.

"I hope that it will be exactly what's promised, and not a scam," he said.

Trump's efforts to cut down on the size of the federal government - with major input from tech billionaire Elon Musk ? have been applauded by many leading Republicans, who control both chambers of Congress.

House Speaker Mike Johnson said during a press conference on Wednesday that the "stewardship of precious American taxpayer dollars" was being well-handled.

"That is a long overdue, much welcome development," he said.

But Trump's efforts to overhaul the federal government - coupled with a number of other major moves, including a crackdown on immigration and his decision to ban diversity, equity and inclusion efforts in government - has also inspired the first nationwide protests against the president this term.

Thousands protested against the reforms across the country on Wednesday.

Numbers were in the dozens at many of the protests, but in demonstrations like Michigan, more than 1,000 people turned out, local media reported. (BBC)

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