Commerce Secretary Wilbur Ross listens during a House Appropriations subcommittee hearing Tuesday in Washington. (Eric Thayer/Bloomberg)

Critics of a Department of Justice request to add a question about citizenship to the 2020 Census are making a furious last-ditch effort to prevent it, saying it will make the decennial count less accurate and more expensive and expressing concerns that the count, which is meant to be nonpartisan, is being politicized by the Trump administration.

Those concerns were exacerbated Monday after the Trump reelection campaign reportedly sent an email to fundraisers asking them to support the president in adding a citizenship question, which critics say could have far-reaching consequences not only on immigrants but also on local economies and political redistricting.

“The President wants the 2020 United States Census to ask people whether or not they are citizens,” read the email, a copy of which was forwarded to The Washington Post by a census advocate. “The President wants to know if you’re on his side.” It includes two answers to click on: ‘Absolutely! Is that even a question?’ and ‘No.’

The Justice Department’s request comes amid controversy surrounding the constitutionally mandated count, which has been beset in the past year by the resignation of its director, charges that it is being underfunded and rumors that the Trump administration sought to appoint a deputy director known for his support of Republican redistricting plans.

The Trump campaign’s email Monday “was the most demoralizing development in this conversation,” said NALEO Educational Fund executive director Arturo Vargas, adding that he and others had been trying to give Republicans the benefit of the doubt that the debate was not inspired by partisan politics.

He and other critics interpreted the email as a sly attempt to rally the president’s base.

“The fact that the Trump campaign would start using this as a fundraiser just really is an assault on the constitution,” which mandates as accurate a count as possible, Vargas said. “It plays to the anti-immigrant nativist sentiments that the Trump campaign used to get elected, and it’s a way to keep that kind of statement alive as the president goes into his second year.”

The executive director of the Donald Trump for President campaign committee did not respond to an email by deadline. Harlan Hill, a member of the campaign’s advisory board, said that, speaking from his own perspective, “We have no idea how many people are in the United States illegally, that’s a tremendous issue. How can we make policy about about an issue that we haven’t yet quantified?”

The email was the latest in several moves by the administration toward adding such a question to the decennial count (annual questionnaires from the Census Bureau that go to about three million Americans already ask whether respondents are citizens). A year ago, a White House draft executive order recommended that the U.S. census ask about immigration status.

The Department of Justice request for the question to be added, obtained in December by ProPublica, said it was necessary to better enforce the Voting Rights Act. That rationale has been echoed by Trump allies.

But the campaign email casts “doubt on the Justice Department’s stated reasons for proposing this untested question at the 11th hour,” Vanita Gupta, president and CEO of the Leadership Conference on Civil and Human Rights, said on Tuesday.

“We now know that support for adding a citizenship question to the 2020 Census goes all the way up to President Trump,” said Gupta, one of the advocates who has lobbied Commerce Secretary Wilbur Ross against the additional question in recent days.

Census experts say the question is not necessary and would depress participation among immigrant communities already leery of the government in the wake of increased crackdowns on illegal immigration. This could result in a less accurate count and add to the cost of the census, as additional efforts would need to be made to reach out to the expected higher number of nonrespondents.

In January, six former census directors who served under Democrat and Republican administrations signed a letter urging Ross not to add the question, noting that it had not gone through the rigorous testing required of new questions.

“It is highly risky to ask untested questions in the context of the complete 2020 Census design,” the letter said, adding that the effect of adding such a question at such a late date “would put the accuracy of the enumeration and success of the census in all communities at grave risk.”

In a letter sent last week to acting assistant attorney general John Gore, 10 Democratic senators expressed concern that such a question would depress participation and demanded to know who initiated the request.

In recent days, Ross has held telephone conversations with census advocates regarding the question, and in a House Appropriations Committee hearing with Ross on Tuesday, several lawmakers urged him to resist adding it. The Census Bureau must by law provide Congress with the final wording of the census questionnaire by March 31.

“We are worried,” Rep. José E. Serrano (D-NY) told Ross at the hearing, referring to the Trump campaign email and adding, “You’re a tough guy. Don’t be afraid to tell somebody, ‘Have you read the Constitution?’”

Ross said at the hearing that the president has requested $3.8 billion for the Census Bureau for fiscal year 2019, $3.1 billion of which would be for the 2020 count. This represents a $2 billion increase over the request for 2018.

Ross, a former census enumerator, did not indicate how he is leaning regarding the citizen question but said that “it is a very big and very controversial request” and that “no political party has asked us to do anything on the census.” He added that he was aware of but had not seen the Trump campaign email.

After Tuesday’s hearing, Rep. Carolyn B. Maloney (D-N.Y.) introduced a bill in the House prohibiting the secretary of commerce from implementing any major changes to the census that have not been researched, studied, tested and submitted to Congress at least three years before census day. It also requires that the Government Accountability Office certify that the subjects and questions included on the census have been researched, studied and tested to the same degree as in previous censuses.