A federal judge ruled Saturday that limits on President Donald Trump's power to fire the head of an independent watchdog agency are constitutional, teeing up a likely Supreme Court showdown.

The case revolves around the White House's 7 February dismissal of Hampton Dellinger, chief of the Office of Special Counsel.

His small agency investigates whistleblower complaints and protects federal workers' rights, among various other roles, and could possibly be a significant player in pushing back against Trump and Elon Musk's efforts to fire swaths of federal employees.

District Judge Amy Berman Jackson had previously ordered Dellinger temporarily reinstated while she considered the case, but on Saturday issued a ruling that his dismissal had been "unlawful."

She said there were specific legal reasons for which the agency head could be fired by the president, but "the curt email from the White House informing the Special Counsel that he was terminated contained no reasons whatsoever."

She further rejected the White House's argument that the unique restrictions blocking the president from firing the special counsel were unconstitutional.

"The elimination of the restrictions... would be fatal to the defining and essential feature of the Office of Special Counsel as it was conceived by Congress and signed into law by the President: its independence," said Jackson.

The case is almost certain to be appealed and eventually end up in the Supreme Court.

The conservative-dominated bench, which includes three Trump-nominated justices, previously declined to block Jackson's temporary reinstatement, saying it would wait for her final ruling.

The Supreme Court is primed to play a significant role in what some experts are suggesting is a looming constitutional crisis as the president tests the limits of his executive power.

Since taking office in January, Trump has launched a campaign led by Musk, the world's richest person, to unilaterally downsize or dismantle swaths of the US government.

Numerous court cases challenging Trump's actions continue to work their way through the courts.