A federal judge blocked the Commerce Department on Tuesday from adding a question on American citizenship to the 2020 census, handing a legal victory to critics who accused the Trump administration of trying to turn the census into a tool to advance Republican political fortunes.

The ruling marks the opening round in a legal battle with potentially profound ramifications for federal policy and for politics at all levels, one that seems certain to reach the Supreme Court before the printing of census forms begins this summer.

A broad coalition of advocacy groups and state and local officials had argued that the citizenship question was effectively forced into the census under false pretenses, in violation of laws enacted to ensure that federal policies heed the public interest.