WASHINGTON (AP) — The Commerce Department says the 2020 U.S. Census will include a question about citizenship status, a move that brought a swift response by the California attorney general to oppose it.

Commerce says in a press release issued Monday night that the citizenship data will help the Justice Department enforce the Voting Rights Act, which protects minority voting rights.

But opponents say the question will discourage immigrants from responding to the census. A coalition of state attorneys general urged the Commerce Department last month to not add such a question, saying it could lower participation among immigrants and cause a population undercount.

The decennial census helps determine political representation in Congress, federal funding of programs and other matters.

Commerce says that between 1820 and 1950, almost every decennial census asked a question on citizenship in some form.

California Attorney General Xavier Becerra said the state will sue the Trump Administration over its decision to add a citizenship question to the 2020 Census.

“We’re prepared to do what we must to protect California from a deficient Census,” he said. “Including a citizenship question on the 2020 census is not just a bad idea — it is illegal.”