NEW YORK (Reuters) - New York, California and other states vowed on Tuesday to stop the U.S. government from asking in the 2020 census whether people are citizens, arguing the question could stop immigrants from participating and skew the makeup of Congress.

The U.S. Census Bureau decided to include the citizenship question in the once-a-decade questionnaire, saying an accurate count of citizens would help protect minority rights under the landmark Voting Rights Act of 1965, according to Commerce Secretary Wilbur Ross.

But liberal opponents feared that the decision would have the opposite effect. They said the move was designed to undercount immigrants, potentially reducing their representation in Congress and federal funding for local jurisdictions, which is determined by population.

“It is a scare tactic to try to scare Latinos and others from participating in the 2020 census,” Arturo Vargas, executive director of the National Association of Latino Elected and Appointed Officials (NALEO) Educational Fund, told reporters.

Pending legal challenges from the states or an unlikely intervention from the Republican-controlled Congress, the citizenship question would appear in the decennial census for the first time since 1950.

New York Attorney General Eric Schneiderman said he would lead a multistate lawsuit to block the decision.

Separately, the State of California filed a lawsuit early Tuesday in federal court against the Commerce Department and the Census Bureau.

The commerce secretary, head of the federal department that runs the Census Bureau, said he authorized the question in response to a Justice Department letter arguing the citizenship question was vital to enforcement of the Voting Rights Act. bit.ly/2pIZlXr

Although a career staff member sent the Justice Department letter, it was conceived by John Gore, a political appointee who as a lawyer in private practice defended multiple Republican redistricting plans, according to emails obtained by ProPublica.

An attendee holds her new country's flag and her naturalization papers as she is sworn in during a U.S. citizenship ceremony in Los Angeles, U.S., July 18, 2017. REUTERS/Mike Blake

Last year, Gore was appointed by Attorney General Jeff Sessions as the head of the Justice Department’s Civil Rights Division, where he reversed the legal challenge to a Texas law that the administration of former President Barack Obama alleged discriminated against minorities.

Justice Department spokesman Devin O’Malley declined to comment on Gore’s involvement. But he said the department looked forward to defending the citizenship question, which he said was needed “to protect the right to vote and ensure free and fair elections for all Americans.”

Vanita Gupta, who ran the Civil Rights Division under the Obama administration, said she questioned the stated motives of President Donald Trump’s administration.

“The Sessions Justice Department is asking for this in the name of voting rights enforcement when it has shown time and time again a reluctance to enforce the Voting Rights Act,” Gupta told reporters.

Other critics said the inclusion of the question would disrupt years of planning that goes into the census. They said there was not enough time to put the question through the rigorous testing that census questions typically undergo to ensure an accurate count.

The U.S. Constitution mandates a census takes place every 10 years, counting every person in the United States.

It is used to determine the allocation to states of seats in the U.S. House of Representatives and to distribute billions of dollars in federal funds to local communities.

“It is facially constitutional to ask the question,” said

James Sample, a law professor at Hofstra University, “even though it is colossally dumb” because it was likely to reduce the number of people responding to the census.

The Trump administration could probably win a legal case, Sample said. But the challenges may succeed if an inaccurate count leads to a range of unconstitutional consequences,

including the unequal distribution of federal funds or potential violations of the “one-person-one-vote” principle, he said.