A federal judge on Thursday blocked Elon Musk’s so-called “department of government efficiency” (Doge) from accessing social security records as part of its hunt under Donald Trump for fraud and waste, calling the effort a “fishing expedition”.

A temporary restraining order was issued by Judge Ellen Hollander, preventing employees of the Social Security Administration (SSA) from granting Doge access to records that contain personally identifiable information. Musk, the world’s richest man and a huge political backer of Trump, has been tasked by the US president with slashing costs and employees at the federal government: a mission that has caused chaos and disruption across the US amid mass firings and huge numbers of government projects and contracts being canceled.

The Trump administration says Doge has a 10-person team of federal employees at the SSA, seven of whom have been granted read-only access to agency systems or personally identifiable information.

The lawsuit challenging Doge’s access to sensitive records was brought in February by the American Federation of State, County and Municipal Employees, the Alliance for Retired Americans and the American Federation of Teachers.

Attorneys for the government argued the Doge access did not deviate significantly from normal practices inside the agency, where employees are routinely allowed to search its databases. But attorneys for the plaintiffs called the access unprecedented.

Hollander also said in her ruling that Doge had to "disgorge and delete" any non-anonymized data it had gotten from the SSA since Trump took office and that the agency could not install or access software in social security systems. Social security payments are a lifeline for millions of elderly Americans across the country and any effort to cut back the system is widely seen as a political minefield. Musk, on the other hand, has asserted that the system is rife with fraud without providing a lot of convincing evidence.