A federal judge’s decision on Tuesday to block the Trump administration’s attempt to add a citizenship question to the 2020 census was hailed by members of Congress and supporters of immigrants.

“Today’s ruling is a win for New Yorkers and Americans across the country who believe in a fair and accurate count of the residents of our nation,” said New York Attorney General Letitia James, whose office filed and led a lawsuit on the issue. “The attempts by the Trump administration to mandate a question about citizenship were not rooted in a desire to strengthen the census process and would only undermine our immigrant communities.”

US District Judge Jesse Furman wrote in a 227-page opinion that Commerce Secretary Wilbur Ross announced his decision of adding the question last March in a way that “concealed its true basis rather than explaining it”, and the decision, even if not unconstitutional, was “unlawful for a multitude of independent reasons and must be set aside”.

The Justice Department, which in December 2017 requested the citizenship question, argued that it would help enforce the Voting Rights Act. Ross, who oversees the census, determined in March that the question is necessary to provide a complete and accurate census block level data.

That led to multiple lawsuits by cities, states, and immigrant rights groups across the US.

Last April, 18 states, 15 cities, and various civil rights groups filed actions in New York, arguing that Ross’ decision violated the Administrative Procedure Act, which regulates federal agencies’ actions and was motivated in part “by invidious discrimination against immigrant communities of color”.

Adding the question would also lead to undercounting of immigrants in the census, claimed the plaintiffs, which might cost their Democrat-leaning communities congressional seats and some $800 billion in federal funding.

While he said that the plaintiffs didn’t prove Ross’ discriminatory intent, Furman questioned Ross and his aides’ incentives and their claim that the question was “well tested.”

The set of testimonies, records and memos related to the issue “are acts and statements of officials with something to hide”, he wrote.

While Ross initially claimed to add the question upon request of the Justice Department, the trial found out that he started the discussion on the issue more than half a year prior. The court infers that they “did have something to hide”, concluded Furman.

The Justice Department, in a statement by spokeswoman Kelly Laco, said: “Secretary Ross, the only person with legal authority over the census, reasonably decided to reinstate a citizenship question on the 2020 census in response to the Department of Justice’s request for better citizenship data, to protect voters against racial discrimination.

“Our government is legally entitled to include a citizenship question on the census, and people in the United States have a legal obligation to answer. Reinstating the citizenship question ultimately protects the right to vote and helps ensure free and fair elections for all Americans,” the statement said.

“This ruling is a forceful rebuke of the Trump administration’s attempt to weaponize the census for an attack on immigrant communities,” said Dale Ho, an American Civil Liberties Union lawyer who represented the plaintiffs.

“Adding a citizenship question was a transparent and unconstitutional effort by the Trump administration to further marginalize vulnerable communities by discouraging them from participating in the census,” said Democratic Congressman Ted Lieu of California. “I’m pleased the court agreed.”

Congresswoman Grace Meng a Democrat from New York and a member of the House Appropriations Committee that funds the US Census Bureau, also hailed the decision, saying that adding the citizenship question would have a decade’s worth of consequences and “deserves to never see the light of day”.

“This was a politically motivated question against immigrant communities,” she said, adding that it would impact the distribution of federal resources and the number of congressional districts in each state.

“Inciting fear in our residents is not only immoral but also ill-conceived,” said New York Attorney General Letitia James.

The Justice Department is expected to appeal the ruling, and the case may head to the Supreme Court later this year.

“Although the Supreme Court will likely have the final say on this issue, we will continue to oppose any attempt to reinstate the citizenship question,” Meng said.