A federal judge on Wednesday heard challenges filed by several states and civil rights groups against the Trump administration’s memorandum to have the Census Bureau exclude undocumented immigrants from being counted in congressional apportionment.

The groups, arguing that such a directive is unconstitutional and likely to have a chilling effect on immigrants’ response to the 2020 Census, said immediate court action was necessary because of the bureau’s announcement this week that door-knocking and other field activities would cease a month earlier than planned.

“That fact makes it even more important to remedy this deterrent effect sooner rather than later,” Matthew Colangelo, chief counsel for federal initiatives for the New York attorney general’s office, told the court. The group argues that reducing the time for data collection will lead to an inaccurate census that undercounts groups that are often hard to count, including minorities, immigrants, low-income households and people with disabilities.

Days after President Trump issued a July 21 directive to the Commerce Department, which oversees the census, to include only U.S. citizens in apportionment, states attorneys general and a coalition of groups led by the American Civil Liberties Union filed to block the move before the counting and analysis is completed.

U.S. District Judge Jesse M. Furman, in a hearing conducted by telephone conference, took up the issue of whether additional judges should hear the matter — in line with federal law that says constitutional challenges over congressional apportionment must be heard by a panel of three district court judges — even though counting is underway and no apportionment has been conducted. The legal dispute centers on the legality of the president’s July 21 memorandum.

Allison Rovner, an assistant U.S. attorney, argued that the claims of potential harm were speculative. Rovner also pushed back on the need for expedited proceedings, arguing that the census is more than half completed. As of Monday, nearly 63 percent of all households have responded, the bureau said.

But that’s exactly why the courts must move quickly, Colangelo said.

“The testimony that we anticipate presenting will show that the presidential memorandum has penetrated immigrant communities [and] there’s a high degree of awareness, and that the awareness of the memorandum will cause — has caused — immigrant families to determine that they cannot trust the federal government with their responses,” Colangelo told the court.

Furman agreed to set a brisk initial schedule for both sides for filing additional arguments and evidentiary material in coming weeks, as requested by the plaintiffs.

The New York attorney general’s office filed its legal challenge July 24, along with several states, counties and cities, including the District, Maryland and Virginia.

The New York Immigration Coalition, joined by the ACLU, the American-Arab Anti-Discrimination Committee, FIEL Houston, and other groups, went to court the same day, arguing that Trump’s “xenophobic” and “lawless” directive runs counter to the Constitution and decades of case law.

“The Fourteenth Amendment mandates ‘counting the whole number of persons’ for congressional apportionment. As the Supreme Court reaffirmed nearly four decades ago, an undocumented individual living in the United States ‘is surely a “a person” in any ordinary sense of that term, ‘whatever his status under the immigration laws,’ ” their brief says, citing Plyler v. Doe.