Washington DC - The Trump administration has reportedly approached the Supreme Court to get the head of a US agency protecting federal staff and whistleblowers fired.

It is the first time that President Donald Trump has resorted to the conservative-dominated court as his blitz to slash public spending and dismantle federal agencies hits legal challenges.

The White House fired Hampton Dellinger on February 7 as head of the Office of Special Counsel, but Dellinger sued the president and a district court ordered he be reinstated.

The US Court of Appeals on Saturday then rejected the Trump administration's request to overrule the decision.

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The emergency appeal filed to the Supreme Court on Sunday branded this an "unprecedented assault on the separation of powers that warrants immediate relief," according to a copy posted online by news outlets.

The appeal added that "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 whom the President believes should not be entrusted with executive power and to prevent the President from relying on his preferred replacement."

It warned that the New York court's intervention "exemplifies a broader, weeks-long trend," adding that the Supreme Court should "not allow the judiciary to govern by temporary restraining order and supplant the political accountability the Constitution ordains."

Trump, who began his second term last month, has launched a campaign led by his top donor Elon Musk to downsize or dismantle swaths of the US government.

The president has faced growing pushback from the courts with around a dozen court orders issued against the administration from some 40 lawsuits. This includes an attempt to freeze $3 trillion in federal grants and loans, a deferred resignation program for government workers, and a plan to transfer incarcerated transgender women to men's prisons.

Trump has also clashed with judges over his abolition of birthright citizenship, sending Venezuelan migrants to Guantanamo Bay, funding cuts to the National Institutes of Health, and placing workers from the US Agency for International Development (USAID) on leave.