Top law enforcement officials in 19 states urged the Commerce Department on Monday to reject a request from the Trump administration to add a citizenship question to the 2020 Census, which they said would be unconstitutional.

“Adding a citizenship question — especially at such a late date in the 2020 Census planning process — would significantly depress participation, causing a population undercount that would disproportionately harm states and cities with large immigrant communities,” the attorneys general wrote. “This undercount would frustrate the Census Bureau’s obligation under the Constitution to determine ‘the whole number of persons in each state,’ threaten our states’ fair representation in Congress, dilute our states’ role in the Electoral College, and deprive our states of their fair share of hundreds of billions of dollars in federal funds that are allocated in part on decennial Census data.”

The letter to Commerce Secretary Wilbur Ross was led by California Attorney General Xavier Becerra, New York Attorney General Eric Schneiderman, and Massachusetts Attorney General Maura Healey.

The attorneys general said adding a citizenship question to the questionnaire would “undermine the accuracy” of the census and reduce response rates. They warned adding the question would hinder the goals of the Voting Rights Act and said states would be negatively impacted by an inaccurate census.

“Because inclusion of a citizenship question would threaten the Census Bureau’s ability to conduct its constitutionally-mandated role, and would be arbitrary and capricious under the Administrative Procedure Act — causing significant, direct harm to our states and residents — we urge you to reject the Justice Department’s request,” the attorneys general wrote.

The Justice Department sent a letter to the Census Bureau in December pushing for a question about citizenship to be included in the 2020 Census. The agency said the question is needed to ensure the 1965 Voting Rights Act is properly enforced.

A citizenship question hasn’t been included in the census since 1950.

In a separate statement, Becerra warned the state of California is prepared to sue the Trump administration if it includes a citizenship question on the 2020 Census.

“What the Trump administration is requesting is not just alarming, it is illegal. The Constitution requires that, every 10 years, we accurately count every person in our country, regardless of citizenship status. This is a sacred responsibility,” Becerra said in a statement. “The California Department of Justice is putting President Trump on notice: if a citizenship question is added to the 2020 U.S. Census Bureau questionnaire, we are prepared to take any and all necessary legal action to protect a full and accurate census.”

Becerra said the request from the Trump administration is “clearly an attempt to bully and discourage our immigrant communities.”