WASHINGTON, United States (AFP) — Two million US federal workers face a deadline of Thursday to quit with a guarantee of eight months’ more paid work or risk being fired on the spot -- a deal derided by labor groups as a “scam” calculated to undermine the civil service.

President Donald Trump’s so-called “A Fork in the Road” initiative, the most sweeping move against federal spending since he returned to office on 20 January, has been wrongly characterized as a “buyout.”

Government “efficiency czar” Elon Musk said it was a chance to “take the vacation you always wanted, or just watch movies and chill, while receiving your full government pay and benefits.”

In fact, employees agreeing to leave could be required to work right through the eight-month period, and failure to resign on Thursday may result in them being fired immediately without compensation.

Labor groups derided the offer as fraught with legal issues and warned against taking it up, questioning whether the government could guarantee the eight months’ pay, given that approved government funding runs out in March.

“Federal employees shouldn’t be misled by slick talk from unelected billionaires and their lackeys,” said Everett Kelley, president of the American Federation of Government Employees (AFGE), in a swipe at Musk.

“Despite claims made to the contrary, this deferred resignation scheme is unfunded, unlawful and comes with no guarantees. We won’t stand by and let our members become the victims of this con.”

US media reported that some 20,000 employees — around one percent of the federal workforce -- had accepted the deal by Wednesday, a fraction of the best expectations of 100,000, which officials said would entail savings of $100 billion.

The AFGE — the largest union for federal employees, representing 800,000 workers — is leading a lawsuit seeking to halt the “arbitrary, unlawful, short-fused ultimatum.”

The complaint, filed in federal court in Massachusetts, casts doubt on assertions that workers would be free to look for other jobs during their deferment periods, citing ethics regulations.

“Not only are these actions illegal and a scam, but they are eroding the health and well-being of our communities,” said Lee Saunders, president of the 1.4 million-member American Federation of State, County and Municipal Employees.

“These workers do everything from making sure families receive their Medicare, Medicaid and Social Security benefits on time to protecting our drinking water and the food we eat to overseeing our national security.”

An employee in the US Office of Personnel Management, granted anonymity to talk frankly, told Agence France-Presse federal workers were mistrustful of advice they were receiving from the administration and felt largely “in the dark” about their options.

“We get what they’re trying to do here. It’s not like we’re pursuing some orderly measure to reduce the size of government,” the employee said.

“No, we’re trying to instill a panic so that people just walk out the door and leave government in a crippled state, which is partly their objective.”