The ruling is the first of a few lawsuits filed around the country that claim the inclusion of a question on citizenship would negatively impact turnout in areas with large immigrant populations.

Census respondents have not been asked whether they are US citizens since 1950, although the query is included in the annual American Community Survey.

The decision to reinstate the question was announced in March 2018, when the commerce secretary Wilbur Ross said it is necessary to "provide complete and accurate census block level data".

The plaintiffs included 18 states, 15 cities and a coalition of non-governmental organisations. US district judge Jesse Furman said in a 277-page opinion document that the decision to include a citizenship question was "unlawful for a multitude of independent reasons".

He said: "Hundreds of thousands — if not millions — of people will go uncounted in the census if the citizenship question is included. The result will not only be a decrease in the quality of census data … but likely also a net differential undercount. That undercount, in turn, will translate into a loss of political power and funds, among other harms, for various plaintiffs."

The decision also violated the Administrative Procedure Act which regulates how federal agencies make decisions, Furman ruled.

The ruling was welcomed by research industry organisation the Insights Association. Howard Fienberg, vice-president of advocacy, said: "The decision is a win: stopping the asking of a question on citizenship in the decennial that hadn’t been properly tested and that was likely to reduce response rates (and thus accuracy) in immigrant communities (both legal and illegal) and in some native American communities."

Fienberg added: "The decision will presumably be appealed, but in the meantime, the Insights Association continues to urge congress to force the issue sooner, taking the question off the table for this decennial."

New York attorney general Letitia James described the ruling as "a win for New Yorkers and Americans across the country who believe in a fair and accurate count of the residents of our nation". 

Kelly Laco, a Justice Department spokeswoman, told Reuters the administration was "disappointed," adding that the "government is legally entitled to include a citizenship question on the census, and people in the United States have a legal obligation to answer."

The case could be reviewed by the Supreme Court.