The suit, filed by unions and advocacy groups, alleges that the email violates laws regarding federal workforce and that the Office of Personnel Management (OPM), which sent the email, does not have the authority to make the demand.

Employees found the email in their inbox on Friday. It asked them to provide a list of five accomplishments for the past week, without revealing classified information.

The message sparked confusion and alarm among workers, particularly after several agency leaders – including Trump appointees – told staff not to respond.

But Musk maintained on X that he was acting on instructions from President Donald Trump and that a failure to reply to the email by Monday night “will be taken as a resignation”.

This meant that, like many of Musk’s directives, federal workers faced uncertainty over their employment. Many also expressed confusion at the competing guidance they had been given by their respective agencies.

Over the weekend, thousands of public health workers at the Department of Health and Human Services (HHS) received a series of conflicting directives regarding the email.

They first received guidance that the instruction was legitimate, and they were told to read and respond to it by Monday, according to an email seen by the BBC.

HHS employees then received an update, directing them to “pause” activities related to the email. HHS officials were working with the administration’s personnel office to comply while being “mindful” of the agency’s sensitive activities, the new guidance said.

“They’re succeeding in driving us insane,” said one employee who works under HHS, and asked not to be named for fear of retaliation.

Staff was still waiting for agency leadership to meet and decide next steps as of Monday, the employee said.

Some federal employees said they had contemplated small acts of rebellion, like responding to the email with recent tasks such as answering hate mail and firing their colleagues.

The US Department of Justice, Department of Defense, and Federal Bureau of Investigation have all recommended their staff not respond to the email, which had a Monday night deadline. All are currently run by Trump appointees and loyalists.

In a statement posted to X, Department of Defense official Darin Selnick told staff to “please pause any response” to the email.

“The Department of Defense is responsible for reviewing the performance of its personnel and it will conduct any review in accordance with its own procedures,” the statement said.

Kash Patel, Donald Trump’s new head of the FBI who has railed against federal employees, also issued a similar direction to the agency’s staff, but the Department of Transportation directed its employees to follow the email’s instructions.

The new lawsuit responding to the email is attached to one filed last week in California, which seeks to block the Trump administration’s mass firing of federal workers.

The revised version alleges that “no OPM rule, regulation, policy, or program has ever, in United States history, purported to require all federal workers to submit reports to OPM”.

Major federal employee unions, including the American Federation of Government Employees, as well as advocacy groups like Vote Vets are part of the lawsuit. A group called the State Democracy Defenders Fund and the California-based Altshuler Berzon law firm represent them.

Musk’s latest tactic to cull federal employees has raised concerns it could reveal classified information or violate government procedures.

“Federal employees have a duty to ensure that sensitive information, data, and records are only used and disclosed for authorized purposes,” American Federation of Government Employees president Everett Kelley wrote to OPM leadership.

Musk and his Department of Government Efficiency have taken aggressive action to cut down the federal workforce. They have bombarded government employees with emails sent via through OPM, threatening layoffs, offering buyouts with questionable terms, dismissing probationary employees, and ordering managers to make lists of employees to cut.

The efforts have sparked anger from within the federal workforce and a barrage of lawsuits, but this latest order has publicly countered from within agency leadership itself.

Max Stier, president of the nonprofit Partnership for Public Service, called the email “yet another example of the new administration’s contempt for public servants and public service that will lead to further confusion, anxiety and waste”.

Trump’s allies have praised the idea of forcing government employees to justify their work.

“I think it’s a great idea, you do it in private business all the time,” Rep Tim Burchett, a Republican from Tennessee, told News Nation. “You have to have accountability.”

He has filed an emergency appeal to the country’s highest court to rule on whether he can fire Hampton Dellinger, head of the US Office of Special Counsel.

It is thought to be the first case related to Trump’s blizzard of executive actions to reach the highest court.

Trump has also cut more than a dozen inspectors general at various federal agencies and fired thousands of employees across the US government.

Mr Dellinger, who was nominated by President Joe Biden, sued the Trump administration after he was fired by email this month.

He argued that his removal broke a law that says he can only be dismissed for poor job performance and that was not given as a reason in the email dismissing him.

The agency lists among its primary objectives the protection of federal employees from unlawful actions in reprisal to whistleblowing, according to its mission statement.

A federal judge in Washington DC issued a temporary order on Wednesday allowing Mr Dellinger to hold on to his position while the case is being considered.

District Judge Amy Berman Jackson said the firing broke US law which tried to ensure the independence of the agency and protect it from political interference.

On Saturday, a divided US Court of Appeals in the nation’s capital rejected the Trump administration’s request to overrule the lower court.

That has led to the justice department filing an emergency appeal to the conservative-dominated Supreme Court, a filing seen by various US media.

“This court should not allow lower courts to seize executive power by dictating to the president how long he must continue employing an agency head against his will,” Sarah M Harris, acting solicitor general, wrote in the filing provided by the Department of Justice to the Washington Post.

“Until now, as far as we are aware, no court in American history has wielded an injunction to force the president to retain an agency head,” the acting solicitor general wrote, according to the Associated Press news agency

The Republican president’s orders on immigration, transgender issues and government spending have also become bogged down in dozens of lawsuits in the lower courts. Those cases may ultimately wind up at the Supreme Court, too.

Trump’s efforts to reduce and reshape the 2.3 million-strong civilian federal workforce continued over the weekend.

Workers in various health agencies who are still within their probation periods received letters on Saturday evening informing them they would be terminated, sources told CBS News, the BBC’s US partner.

“Unfortunately, the agency finds that you are not fit for continued employment because your ability, knowledge and skills do not fit the agency’s current needs, and your performance has not been adequate to justify further employment at the agency,” read the letters.

At least 9,500 workers at the departments of Health and Human Services, Energy, Veterans Affairs, Interior and Agriculture have been fired by Trump, according to a tally from Reuters news agency.

Another 75,000 workers have taken a buyout offered to get them to leave voluntarily, according to the White House.

The cost-cutting initiative has been led by department of government efficiency, or Doge, a task force led by Elon Musk.

Democrats have decried Musk, the world’s richest man, as unelected and his actions as too sweeping – a “hostile takeover” in the words of the party’s Senate leader Chuck Schumer.