New York Attorney General Eric Schneiderman (D) filed a federal lawsuit on Tuesday aimed at blocking the Trump administration from adding a question about citizenship to the 2020 census , saying such a question violates the U.S. Constitutions mandate to count all persons.

In a statement, Schneidermans office said the suit was filed on behalf of 17 states plus the District of Columbia, six cities and the U.S. Conference of Mayors. It comes a little over a week after the Commerce Department, which oversees the Census Bureau, announced it would add the question. Schneiderman said the decision to add a citizenship question blatantly undermined the Constitutions mandate to count all people.

The prospect of someone saying, I am from the Trump administration knocking on your door to ask a question about citizenship would understandably provoke real fear, Schneiderman said during a Tuesday press conference, flanked by members of New Yorks congressional delegation.

The numbers from the census are used to determine how many seats each state gets in Congress, as well as how hundreds of billions of dollars in federal funds are allocated. Democratic members of New Yorks congressional delegation said Tuesday that the decision to add a citizenship question was an attack on states, like New York, with high immigrant populations in an attempt to cut their congressional representation and share of federal funding.

It is being added to harm states and cities like New York both politically and financially, said Rep. Carolyn Maloney (D-N.Y.). We are being unfairly targeted because we have large, diverse immigrant populations which we welcome and support.

Civil rights groups voiced loud opposition to adding the question, noting that the bureau has not tested the question and that immigrant groups will be afraid to respond out of fear about their immigration status. In September, census researchers reported they were already seeing an unprecedented amount of concern about the confidentiality of census responses amid the Trump administrations harsh immigration rhetoric and policies.

The census already asks Americans about their citizenship as part of the American Community Survey, a smaller annual survey that goes out to about 3 million people. The Department of Justice asked the Commerce Department to add a citizenship question to the 2020 census, saying it needed better information to better enforce Section 2 the Voting Rights Act, the landmark 1965 law designed to protect the voting power of minorities. Section 2 prohibits discriminatory voting practices.

The census has not asked about citizenship on the decennial form since 1950, and former top Justice Department officials say that the ACS provides adequate data to enforce the law.

On Tuesday, Schneiderman questioned whether U.S. Attorney General Jeff Sessions was really interested in better enforcing the Voting Rights Act.

Jeff Sessions has not brought one case under Section 2 of the Voting Rights Act since hes been Attorney General, he said.

A Commerce Department spokesman expressed confidence that the decision to add the citizenship question would withstand legal scrutiny.

We are not going to comment on the specifics of pending litigation, but these cases are without merit. We look forward to prevailing in court and continuing to work with the Census Bureau to conduct a complete and accurate 2020 census, the spokesman said.

This post has been updated.