President Donald Trump signed a presidential memo Tuesday aiming to exclude the number of undocumented immigrant populations when redistributing congressional seats following the 2020 census.

The unprecedented move, which civil rights advocates say is unconstitutional, comes a year after the Trump administration tried and failed to include a citizenship question in the census. If implemented, the measure would diminish the political power of areas with more concentrated immigrant populations, which often vote Democratic.

Trump’s move is prompting legal action from groups including the American Civil Liberties Union and New York and California, all of whom also litigated the originally proposed citizenship question.

“His latest attempt to weaponize the census for an attack on immigrant communities will be found unconstitutional. We’ll see him in court, and win, again,” said Dale Ho, director of the ACLU’s Voting Rights Project.

After the Trump administration announced a citizenship question last year, immigrant rights groups challenged the proposal in a suit that ultimately arrived at the Supreme Court. Chief Justice John Roberts ruled with the liberals, writing that the administration’s attempt to include a citizenship question was “contrived.”

Despite the question being struck down and immigrant advocacy groups’ vigorous outreach, activists are still worried that undocumented immigrants and mixed-status families may have lingering fears about the question and not respond to the census.

Without the citizenship question, the Trump administration is trying to gather the information from states through driver’s license and state identification data, which do include citizenship status. So far, the administration has agreements with Iowa, Nebraska, South Carolina, and South Dakota to gather the data.

As written in the Constitution, the census ultimately falls under Congress’s authority, not the president’s. In the 14th Amendment, which repealed the racist “three-fifth” clause in the original document, the census is required to count the “whole number of persons in each state,” not only citizens or residents with documentation.

Democratic leadership in Congress have also released statements pushing back on the move, with Speaker of the House Nancy Pelosi pledging that the House will fight the order.

“Trump’s unlawful effort is designed to again inject fear and distrust into vulnerable and traditionally undercounted communities, while sowing chaos with the Census,” Pelosi said. “The House of Representatives will vigorously contest the President’s unconstitutional and unlawful attempt to impair the Census.”