Washington DC - A judge on Thursday denied a union bid to temporarily halt the firing of thousands of federal employees on probationary status, handing President Donald Trump another legal win in his plan to slash the government workforce.

District Judge Christopher Cooper said he lacked the jurisdiction to handle the complaint, one of several filed in courts in recent days in an effort to pause the mass sackings.

The judge's decision comes as around 6,700 workers at the 100,000-strong Internal Revenue Service (IRS) who were on probation were being laid off.

A former IRS official said most of the IRS employees being let go worked in the tax agency's enforcement teams, less than two months before the US income tax filing deadline of April 15.

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A number of IRS employees posted messages on LinkedIn saying they had been abruptly terminated and were seeking other opportunities.

The National Treasury Employees Union and four other unions that represent federal employees had asked Cooper to issue a temporary restraining order preventing the termination of their members who are probationary employees.

Cooper, an appointee of former president Barack Obama, said his court lacks jurisdiction to hear their claims and they should instead be brought before the Federal Labor Relations Authority, a body that adjudicates federal labor disputes.

"Federal district judges are duty-bound to decide legal issues based on even-handed application of law and precedent – no matter the identity of the litigants or, regrettably at times, the consequences of their rulings for average people," the judge said.

In his opinion, Cooper said the federal government employs 220,000 probationary employees, and he noted that workers with that status at the Food and Drug Administration, the Department of Energy, the Environmental Protection Agency, the National Park Service, and other agencies have already been sacked.

On Wednesday, another federal judge declined a request to temporarily block Elon Musk and his Department of Government Efficiency (DOGE) from firing federal employees.