US District Judge Paul Engelmayer in Manhattan issued the order on Saturday after a coalition of Democratic attorneys general from 19 US states filed a lawsuit late on Friday arguing Musk's Department of Government Efficiency has no legal power to access the US Department of Treasury systems.
The ruling also applied to other political appointees of President Donald Trump's administration.
Hours after it was issued, Musk called it "absolutely insane!" in a post on X.
The billionaire said the Treasury Department and DOGE had agreed to require all outgoing government payments to include a rationale in the form of a comment and to have a categorisation code.
Musk also said that a do-not-pay list of entities that should not receive government payments should be updated at least weekly, if not daily.
The changes, Musk said on X, were "obvious and necessary" and being implemented by government employees, and not by anyone from DOGE.
The lawsuit said Musk and his team could disrupt federal funding for health clinics, pre-schools, climate initiatives, and other programs, and that Trump could use the information to further his political agenda.
DOGE's access to the system also "poses huge cybersecurity risks that put vast amounts of funding for the States and their residents in peril," the state attorneys-general said. They sought a temporary restraining order blocking DOGE's access.
The judge said the states' claims were "particularly strong" and warranted him acting on their request for emergency relief pending a further hearing before another judge on February 14.
"That is both because of the risk that the new policy presents of the disclosure of sensitive and confidential information and the heightened risk that the systems in question will be more vulnerable than before to hacking," Engelmayer wrote.
New York Attorney-General Letitia James, a Democrat whose office is leading the case, welcomed the ruling, saying nobody was above the law and that Americans across the country had been horrified by the DOGE team's unfettered access to their data.
"We knew the Trump administration's choice to give this access to unauthorized individuals was illegal, and this morning, a federal court agreed," James said in a statement.
"Now, Americans can trust that Musk – the world's richest man – and his friends will not have free rein over their personal information while our lawsuit proceeds."
Engelmayer's order bars access from being granted to Treasury Department payment and data systems by political appointees, special government employees and government employees detailed from an agency outside the Treasury Department.
The judge also directed that anyone prohibited under his order from accessing those systems to immediately destroy anything they copied or downloaded.
Trump deputised Musk to lead DOGE to identify fraud and waste in the government.
Musk's efforts have alarmed Democrats and advocacy groups who say he is overstepping his authority by seeking to dismantle agencies responsible for critical government programs and fire federal workers en masse.
Treasury Secretary Scott Bessent, a Trump appointee, said this week that the department's payment system will not be touched by Musk and that any decisions to stop payments would be made by other agencies.
