The Trump administration is following through on its plans to include a question about citizenship on the 2020 Census, an effort Democrats have decried as an attempt to suppress California's population reporting and cost the state at least one congressional seat.

Commerce Secretary Wilbur Ross on Monday night announced the decision to include the citizenship question over the objections of Democrats and civil rights groups in a post on the Commerce Department website.

Ross cast the decision as a "reinstatement" of the citizenship question, which last appeared on the decennial census in 1950. He argued that collecting citizenship data has been a "long-standing historical practice" and continues among sample populations in the regular Census "to this day."

In response to a request from the Department of Justice to include the citizenship question, Ross said he has spent months considering all the "facts and data relevant to the question," including a comprehensive review commenced by the Census bureau.

Ross said he had determined that including the question would provide the most "complete and accurate" citizen voting age population (CVAP) data. The DOJ and the courts use CVAP data for the enforcement of Section 2 of the Voting Rights Act, which prohibits the drawing of election districts in ways that improperly dilute minorities' voting power.

Ross argued that the additional question wouldn't create an added imposition for the approximately 90 percent of the U.S. population who are citizens. He also said it wouldn't overly burden the non-citizens because approximately 70 percent of them already answer the question correctly on the annual American Community Survey, an ongoing survey of U.S. population that generates data that help determine how more than $675 billion in federal and state funds distributed every year.

He stressed that the question poses no additional imposition because "census responses by law may only be used anonymously and for statistical purposes."

Democrats have vowed to fight the inclusion of the question, viewing the decision as another front in the Trump administration's ongoing war with California over illegal immigration and the state's passage of so-called sanctuary laws that limit local law enforcement communication with federal immigration authorities.

They argue that adding the question would result in depressing populations in areas with a high number of illegal immigrants because they would be afraid to fill out the questionnaire out of fear that the federal government would use it to locate them and try to deport them and their loved ones.

California Attorney General Xavier Becerra Monday night said he would be "filing suit" against the Trump administration's decision.

"Including the question is not just a bad idea—it's illegal," Becerra tweeted, and included a San Francisco Chronicle op-ed he co-wrote with Alex Padilla, California's secretary of state titled "Citizenship question on 2020 census may result in undercount."

Becerra is one of 17 Democratic state attorneys general who wrote Ross a letter last month, arguing that including the citizenship question would be unconstitutional and would scare illegal immigrants into not participating in the decennial questionnaire and result in an undercount of the population.

"This undercount would frustrate the Census Bureau's obligation under the Constitution to determine ‘the whole number of persons in each state,' threaten our states' fair representation in Congress, dilute our states' role in the Electoral College, and deprive our states of their fair share of hundreds of billions of dollars in federal funds that are allocated in part on decennial Census data," the attorneys general argued.

After Ross's decision became public Monday night, several civil rights groups denounced it and pledged to work to overturn its inclusion.

"This was the wrong decision. Despite overwhelming bipartisan and multi-sector opposition, Secretary Ross capitulated to President Trump and Attorney General Sessions," Vanita Gupta, president and CEO of the Leadership Conference on Civil and Human Rights said in a statement.

"This untimely, unnecessary, and untested citizenship question will disrupt planning at a critical point, undermine years of painstaking preparation, and increase costs significantly, putting a successful, accurate count at risk," she said. "We will work with our coalition, the business community, bipartisan state and local officials, and other civic leaders to overturn this ill-advised decision."

Three Republican senators on Tuesday applauded the move, calling it a commonsense addition and the only way to achieve an accurate count of the country's citizens.

Sens. Ted Cruz of Texas, Tom Cotton of Arkansas, and James Inhofe of Oklahoma argue that accurate census data is a vital part of the country's democracy. The trio said they previously sent a letter to Ross imploring him to add the citizenship question.

"I applaud Secretary Ross for honoring this request by my colleagues and me," Cruz said in a statement. "It is imperative that the data gathered in this census is reliable, given the wide-ranging impacts it will have on U.S. policy."

"A question on citizenship is a reasonable, commonsense addition to the census," he added.

"Counting the number of U.S. citizens in the country should be a high priority of the census, and the only way to get an accurate count is to add a question about citizenship to the census itself," Cotton said.

UPDATE 10:00 A.M.: Comment from senators has been added.