New York state Attorney General Eric Schneiderman on Tuesday announced that 17 states and Washington, D.C. filed a federal lawsuit over the Trump administration’s decision to add a question about citizenship to the 2020 census.

In the lawsuit, filed in the U.S. District Court for the Southern District of New York, the states argue that the decision to ask about citizenship status will not properly carry out the Constitution’s Enumeration Clause, which states that the “actual enumeration” of people in the United States be used to determine congressional districts. The lawsuit also argues that the decision runs up against the Administrative Procedure Act, which bars “arbitrary and capricious” agency action.

“This is a blatant effort to undermine the census,” Schneiderman said in a press conference announcing the lawsuit, adding that the lawsuit filed by several states will block the decision to include the citizenship.

Seventeen states were included in the lawsuit against the Trump administration: New York, Connecticut, Delaware, Illinois, Iowa, Maryland, Minnestoa, New Jersey, New Mexico, North Carolina, Oregon, Rhode Island, Vermont, Washington, Massachusetts, Pennsylvania, and Virginia, as well as Washington, D.C.. The cities of Chicago, New York, Philadelphia, Providence, Sanfrancisco, and Seattle, as well as the U.S. Conference of Mayors, also joined the lawsuit.

The Commerce Department announced last month that the 2020 census will include a questions about citizenship status, which experts warn could discourage some residents from participating in the survey and lead to an undercount of the U.S. population.

Schneiderman noted in the press conference that the citizenship question could lead to an inaccurate count, and in turn change the number of congressional representatives representing certain areas and reduce federal funding to certain regions. The lawsuit argues that the “unconstitutional and arbitrary decision to add a citizenship demand to the 2020 census questionnaire, which will fatally undermine the accuracy of the population count and cast tremendous harms to Plaintiffs and their residents.”

The lawsuit also argues that anti-immigrant policies promoted by the Trump administration will “amplify the negative impacts on census participation rates” from the citizenship question.

The Trump administration decided to add the citizenship question late in the process for developing the 2020 questionnaire, and the Commerce Department chose to add the question despite research from the Census Bureau concluding that such a change to the questionaire could depress response rates, which the lawsuit filed Tuesday also notes. The lawsuit argues that the Trump administration violated the Administrative Procedure Act by failing to conduct proper tests about the effect of the citizenship question and by failing to offer a convincing argument for including the question.

Read the complaint: