US President Donald Trump's administration has asked the Supreme Court to let it withhold more than $4bn (£3bn) in foreign aid.
The administration is seeking an emergency order as it tries to claw back funds for foreign assistance programmes that have already been allocated by Congress.
A lower court last week said the Trump administration had a statutory obligation to spend the money, and an appeals court declined last Friday to freeze that ruling.
The president attempted to use a rarely used legislative tool to withdraw the funds. Since returning to the White House, Trump has cancelled billions of dollars in foreign aid that he says does not align with his objectives.
Solicitor General D John Sauer said in Monday's filing that the lower court's injunction "raises a grave and urgent threat to the separation of powers".
