The US Supreme Court on Tuesday blocked a lower court's order requiring the Trump administration to reinstate thousands of fired federal probationary workers.

The conservative-majority top court said the non-profit organizations that filed the case seeking to halt the mass firings lacked legal standing to bring the lawsuit.

William Alsup, a district judge in California, ordered six federal agencies last month to rehire 16,000 probationary workers who were laid off as part of President Donald Trump's push to slash the size and scope of government.

Alsup said the justification of "poor performance" given for the mass firings was a "sham" and he ordered the departments of the Treasury, Veterans Affairs, Agriculture, Defense, Energy and Interior to reinstate fired probationary employees.

The Supreme Court, in a temporary victory for the Trump administration, blocked Alsup's order while litigation in the case continues.

In a 7-2 ruling, the court said the judge's order "was based solely on the allegations of the nine non-profit-organization plaintiffs in this case.

"But under established law, those allegations are presently insufficient to support the organizations' standing," it said.

Since returning to the Oval Office in January, Trump has taken an ax to the US government, cutting spending programs and firing tens of thousands of the more-than two million employees on the federal payroll.