By law, the federal government must give its workers at least 30-days notice that it is laying them off.

After Vought’s tweet, major departments such as Treasury and Health and Human Services (HHS) confirmed they were issuing notices to employees, and Homeland Security, where many of its employees are considered essential, said it would lay off workers at its Cybersecurity and Infrastructure Security Agency.

But exact details were scarce.

Two major unions, the American Federation of Government Employees and AFL-CIO, had filed a lawsuit challenging the legality of Vought’s announced plans to carry out layoffs during the shutdown.

On Friday, once he said the process had begun, they asked a federal court in Northern California to temporarily block the move.

“It is disgraceful that the Trump administration has used the government shutdown as an excuse to illegally fire thousands of workers who provide critical services to communities across the country,” AFGE president Everett Kelley said.

In its opposition to the temporary restraining order, lawyers for the OMB revealed which agencies and how many of their employees would be affected first, indicating an estimated 4,600 employees would receive RIF notices starting on Friday.

“The President, through OMB, has determined that agencies should operate more efficiently and has directed them to consider steps to optimize their workforces in light of the ongoing lapse in appropriations,” the justice department attorneys argued in the filing.

More than a quarter of the cuts would be made at the Treasury Department, where notices were being sent to approximately 1,446 employees.

HHS was notifying between 1,100 and 1,200 employees, the filing said.

The Department of Education and Department of Housing and Urban Development intended to lay off at least 400 employees apiece, while the Departments of Commerce, Energy, Housing and Urban Development and Homeland Security each planned cuts ranging between 176 to 315 employees, according to the filing.

There was no indication about how many notices the agencies issued on Friday.

The filing also said that 20 to 30 at the Environmental Protection Agency were issued “intent to RIF” notice on Friday, notifying them that they may be affected in the future. Other federal agencies might also make cuts.

The government lawyers said the labour unions had failed to establish that their members would be irreparably harmed by the layoffs, which is needed for the judge to grant the restraining order. But they said a restraining order would “irreparably harm the government”.

A temporary restraining order would prevent agencies “determining how best to organize their workforces”, they argued, noting that the government has traditionally been granted the widest latitude in the “dispatch of its own internal affairs”.

The layoffs are unprecedented. In past shutdowns, furloughed employees returned to work when the government reopened and were paid retroactively for their time away.

Both furloughed and “essential” workers who must still carry out their job duties are not paid when government funding is temporarily cut off.

The current shutdown began 10 days ago, after lawmakers failed to reach a deal on a funding measure to keep the government open.

“They held off for 10 days,” Republican Senator John Thune told reporters, referring to the White House. “At some point they were going to have to make some of these decisions and prioritise where they’re going to spend money when the government is shut down.”

Senate Minority Leader Chuck Schumer, a Democrat, accused Trump and Vought of causing “deliberate chaos”.

Democrats have refused to vote for a Republican spending plan that would reopen the government, saying any resolution must preserve expiring tax credits that reduce health insurance costs for millions of Americans and reverse Trump’s cuts to Medicaid, the healthcare program for elderly and low-income people.

Republicans accuse Democrats of unnecessarily bringing the government to a halt, and blame them for the knock-on effects caused by the federal work stoppage.

A shutdown meant that “non-essential” federal workers would be placed on unpaid leave. It is currently affecting about 40% of the federal workforce – about 750,000 people.

Furloughed employees are legally supposed to receive back-pay after a shutdown ends and they return to work, but the Trump administration has insinuated this might not happen.

Significantly culling the federal workforce has been a long-term priority for Vought.

The president and his budget chief have greeted the shutdown as a unique opportunity to make further firings on top of the thousands of cuts they have made since Trump returned to office in January through a combination of firings, buyouts, administrative leave and resignations.

The Partnership for Public Service, a bipartisan group studying the government, estimated the federal workforce had been reduced by about 200,000 employees as of 23 September.

Career services firm Challenger, Gray & Christmas, reported last month that the government sector had announced 299,755 planned job cuts this year, of which 289,363 were federal workers impacted by the Department of Government Efficiency (Doge), the White House cost-cutting effort initially led by billionaire Elon Musk.

Before the shutdown, Vought’s office instructed federal agencies to prepare reduction-in-force plans aimed at cutting employees or programmes whose funding might lapse or were “not consistent with the President’s priorities”, Politico reported.

One day after the shutdown began, Trump posted on Truth Social that he had met with Vought “to determine which of the many Democrat Agencies, most of which are a political SCAM, he recommends to be cut, and whether or not those cuts will be temporary or permanent.”