Dozens of US states, cities and counties on Friday urged a federal court to block President Donald Trump from carrying out what they called a "flagrantly unconstitutional" directive to exclude undocumented immigrants when apportioning congressional seats.
Led by New York state, the mostly Democratic-leaning plaintiffs said in a Manhattan federal court filing the July 21 directive should be declared unconstitutional, or that a preliminary injunction be entered against its enforcement.
They called the directive the latest in a string of White House attacks on immigrant communities, and alleged that a "plainly xenophobic and discriminatory purpose" animated the administration's "exclusionary policy."
The White House was not immediately available for comment. Trump's response is due by August 17.
At stake is the makeup of the 435-member House of Representatives, now controlled by Democrats.
While the Census Bureau estimates the US population at 330.1 million, the plaintiffs said the directive could exclude several million people from being counted, potentially shifting a few House seats to Republican-leaning states.
The plaintiffs have said everyone in the United States must be counted, saying the Constitution requires a count based on the "whole number of persons" in each state.
They have also said Trump's directive could also distort the decennial census by deterring immigrants from responding.
But Trump has said "person" had never been understood to include anyone physically present in a state, and called alleged efforts to conceal undocumented immigrants "part of a broader left-wing effort" to erode Americans' rights.
Census data are also used to allocate hundreds of billions of dollars in federal funds annually, and in redistricting.
Illinois, Massachusetts, Michigan, New Jersey, Pennsylvania, New York City, Chicago, Philadelphia, San Francisco and several immigrants' rights advocates are among the nearly four dozen plaintiffs. California has filed a similar, separate lawsuit.
The judge now overseeing the case on Friday asked that a three-judge panel be designated to address the complaint, citing laws requiring such panels in some apportionment cases.