Los Angeles, California - A US judge blocked a California law on Monday that would have prohibited federal immigration agents from covering their faces during operations, but upheld that they must display identification.

The use of masks by some unidentified and heavily armed US Immigration and Customs Enforcement officers has stoked criticism from local leaders in Democratic-run cities.

US District Judge Christina Snyder found California's masking law, known as the "No Secret Police Act," to be discriminatory as it did not apply to state law enforcement officers.

The proposed ban "unlawfully discriminates against federal officers," she wrote in the ruling.

US Attorney General Pam Bondi branded the move a win on social media after her Justice Department challenged the law.

"We will continue fighting and winning in court for President Trump's law-and-order agenda – and we will ALWAYS have the backs of our great federal law enforcement officers," she wrote in a post on X.

But Snyder upheld a measure that requires agents to show identification and their badge numbers, which California Governor Gavin Newsom claimed as a partial victory.

"A federal court just upheld California's law REQUIRING federal agents to identify themselves. California will keep standing up for civil rights and our democracy," he wrote on X.

The state's attorney general Rob Bonta also welcomed the decision which would deny the Trump administration's "attempt to block California from requiring law enforcement officers" from visually identifying themselves, he wrote in a statement.

"Safe communities thrive on transparency and trust and California is committed to doing our part to uphold public safety and civil liberties."

Snyder suggested in her ruling that the ban would be constitutional if broadened to cover state law enforcement as well.

Democratic State Senator Scott Wiener, who co-authored the ban's legislation, said Monday he would amend the law and propose a new ban that would include all state law enforcement officials.

"Now that the Court has made clear that state officers must be included, I am immediately introducing new legislation to include state officers," he wrote in a statement.

"I will do everything in my power to expedite passage of this adjustment to the No Secret Police Act."