Updated 4:05 p.m. ET, July 19

The Mexican American Legal Defense and Educational Fund is asking a federal judge in Alabama to allow a group of Latino voters and the advocacy group Chicanos Por La Causa to defend a lawsuit challenging the U.S. Census Bureau's policy of including unauthorized immigrants in census numbers used to redistribute seats in Congress. The city of San Jose, Calif., Santa Clara County in California and King County in Washington joined them and filed a similar motion in court on July 17.

Once a decade, the bureau counts every person living in the U.S. — regardless of immigration status — for the census required by the Constitution, as the Census Bureau's acting director recently told NPR. After the Civil War, the 14th Amendment was ratified to mandate the counting of "the whole number of persons" in each state.

That population tally determines the number of seats in the House of Representatives, as well as Electoral College votes in presidential elections, that each state gets.

In May, the state of Alabama and Republican Rep. Mo Brooks filed a lawsuit in the U.S. District Court for the Northern District of Alabama. They argue that the framers of the Constitution did not intend for the census numbers to include immigrants living in the U.S. illegally. In their complaint, Alabama Attorney General Steve Marshall, a Republican, alleges that after the upcoming 2020 census, the state may lose one of its seven congressional seats and one of its nine Electoral College votes to a state with a higher population of unauthorized immigrants.

Alabama's complaint calls for the Census Bureau to exclude unauthorized immigrants from census numbers used for reapportionment.

"Adding a question regarding immigration status [to the census questionnaire] is one of several possible methods of excluding illegal aliens from the count used for apportionment," says a spokesperson for Alabama's attorney general, Mike Lewis, in an email.

"The reason why this has become so much more of an issue now than maybe it would have, you know, however many years ago is really the number of those who are in this country currently illegally," Marshall said in June after a House Judiciary subcommittee hearing on the census where he testified about the lawsuit. "It's part of, I guess, a little bit of the national debate that we have right now about the enforcement of our immigration laws and what we've allowed."

The Justice Department has assigned one of its attorneys, Brad Rosenberg, to the case. But the Trump administration has not yet filed a response to the complaint, which is due in court by Sept. 13, after a federal judge granted Rosenberg's request to extend the original deadline. A DOJ spokesperson, Devin O'Malley, declined to comment on when the department plans to file its reply and on the motions to intervene.

At a House Oversight and Government Reform Committee hearing in May on the new citizenship question on the 2020 census, the acting head of the Justice Department's civil rights division, John Gore, was asked by Rep. Gary Palmer, R-Ala., to comment on the importance of knowing the citizenship status of people counted for congressional reapportionment.

"I think that is a very important question and a very important issue," Gore replied. "It's not one that the Department of Justice has taken a position on."

The federal government's largest statistical agency has long included citizens of foreign countries living in the U.S. in national population counts.

"We have real concerns about whether the Trump administration, which is the defendant in the case, would actually put forward a vigorous defense of their continued counting of all persons as persons," says Thomas Saenz, the president and general counsel of MALDEF.

On July 12, MALDEF filed a motion to intervene in the case on behalf of Chicanos Por La Causa and individual Latino voters from Arizona, California, Florida and Texas — states with high populations of Latino residents and unauthorized immigrants. In the court filing, Saenz argues that excluding unauthorized immigrants from census numbers could deny the communities where they live fair political representation.

"This is really attempting to reopen a debate that we haven't had in this country since the Civil War," he says, noting the original language in the Constitution specifying that enslaved people should be counted as "three fifths of all other Persons."

Attorneys for the city of San Jose, Calif., California's Santa Clara County and Washington's King County say their plaintiffs can lose access to federal dollars tied to census numbers if unauthorized immigrants are excluded from their population counts.

"Each of these jurisdictions is home to vibrant immigrant communities that also happen to include large numbers of undocumented people," says Kristen Clarke, president and executive director of the National Lawyers' Committee for Civil Rights Under Law, one of the legal groups representing San Jose and the two counties. "They too stand to lose a significant share of federal funding if Alabama prevails in this case."

Their court filing cites NPR's recent interview with the Census Bureau's Acting Director Ron Jarmin, who noted that "whether it's funding for streets or for schools or for health care, decisions throughout the federal government are made based on the population of the local communities that people live in."

Alabama's lawsuit against the Census Bureau comes as the agency is facing six separate lawsuits over a decision by Commerce Secretary Wilbur Ross, who oversees the bureau, to add a controversial question about U.S. citizenship status to the 2020 census. More than two dozen states and cities, as well as other groups, want the question removed because of fears of discouraging noncitizens from participating and harming the accuracy of the head count.

While Ross has said the Justice Department needs responses from the citizenship question to better enforce the Voting Rights Act, a federal judge in New York City has said internal documents the Trump administration released suggest the decision to add the question may be politically motivated. In an email to Ross, Kansas Secretary of State Kris Kobach suggested wording for a census citizenship question that asks noncitizens about their immigration status, after highlighting "the problem that aliens who do not actually 'reside' in the United States are still counted for congressional reapportionment purposes."

The Census Bureau referred a request for comment about the motions to intervene to the Commerce Department, which is also named in the Alabama lawsuit. A spokesperson for Commerce declined to comment.

A spokesperson for Brooks deferred to the Alabama's attorney general's office for comment on MALDEF's filing, but a spokesperson for Marshall also declined to comment. Neither spokesperson has responded to NPR's inquiries about the motion by attorneys for San Jose, California's Santa Clara County and Washington's King County.

Asked by a reporter after the House hearing in June whether he has any expectation that the Trump administration will defend the Census Bureau in this lawsuit, Brooks told NPR that he had not spoken with anyone in the administration about what position it will take.

"The Trump administration itself is going to have to decide whether they want to reward sanctuary states by giving them more congressional seats and more Electoral College votes than they would be due based solely on account of American citizens or foreigners who are lawfully in the U.S.," he said.

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