Democratic attorneys general in at least 12 states have announced that they will bring legal action to try to stop the Trump administration from adding a question on citizenship to the 2020 U.S. census. Opponents of the question say it would decrease responses from both undocumented and legal immigrants. Some critics have suggested that the administration wants to add the question to reduce the population count in Democratic areas that are home to large numbers of immigrants.

The move is in response to the administration’s announcement Tuesday that it will include a question on the census that asks whether respondents are American citizens, a question that has not appeared on the questionnaires since 1950.

The Hill reports:

An undercount could put at risk billions of dollars in federal aid, in programs ranging from health care to education and even law enforcement funding for some states. Figures from the census are used to allocate federal money through programs across the government. … Research shows that more than 60 percent of the estimated 11 million undocumented immigrants living in the United States live in just 20 metro areas across the country. Twelve of those 20 metro areas are in blue states that backed Democratic nominee Hillary Clinton by wide margins in the 2016 presidential election. More than a million undocumented immigrants live in the New York area, and a million more live in Los Angeles, according to a 2017 study by the Pew Research Center. Chicago, Washington, D.C., Seattle, Denver and four California metro areas all have between 100,000 and 400,000 undocumented immigrant residents.

“The census is supposed to count everyone,” said Attorney General Maura Healey of Massachusetts. “This is a blatant and illegal attempt by the Trump administration to undermine that goal, which will result in an undercount of the population and threaten federal funding for our state and cities.”

New York Attorney General Eric Schneiderman, who has said he will lead the multi-state effort against the new census question, echoed Healey’s sentiment in a statement, writing: “This move directly targets states like New York that have large, thriving immigrant populations—threatening billions of dollars in federal funding for New York as well as fair representation in Congress and the electoral college.”

California state Attorney General Xavier Becerra, who has announced that he too will file a suit to stop the question, said: “We’re hoping that [what] we do is win this lawsuit, remove a very biased question from the census and then do everything we can to get people to participate.” Becerra and California Secretary of State Alex Padilla co-authored an op-ed in the San Francisco Chronicle about the lawsuit.

The Constitution requires that every resident of the U.S. be counted in the decennial census, regardless of whether they are citizens. The data is used to redraw boundaries for political districts, school boards and House seats, and to allocate federal grants and subsidies to where the need is greatest.

Kathay Feng, the executive director of California Common Cause and a leader for nonpartisan reformation of California’s redistricting process, spoke to Ian Masters on the widely broadcast radio talk show “Background Briefing” about the new census question. She said:

“There’s a huge demographic change [happening] in this country. One way for a particular party, and I’m just going to say it, the Republican Party, to fight that demographic change is by making sure that only certain people can participate … by adding a citizenship question, we can either scare off other people from filling it out, or create such a skewed result that now that number that comes from each state … can reflect the number that some people would like to see, which is a portion.”

She added that “when you start to skew that way, what you do is you have really foreclosed a huge population of people.”

Legal experts say it is not yet clear whether the states will be successful in challenging the question in court.