WASHINGTON (AFP) - The United States is gearing up to conduct its next population census in 2020 but a thorny question on citizenship has ignited controversy even before it has begun.
When the decennial national headcount gets under way, census takers may have to ask respondents if they are US citizens, which observers say would discourage some ethnic minorities from participating and undermine the accuracy of the data.
Mr Arturo Vargas, head of the NALEO (National Association of Latino Elected and Appointed Officials) Educational Fund, said surveys have shown as recently as September last year that test respondents are now experiencing "unprecedented fear of the US government".
President Donald Trump took office on a nationalist anti-immigrant agenda, linking foreigners and migration to terrorism, crime and lost jobs. In his State of the Union address last month he reiterated his pledge to cut legal immigration and beef up enforcement.
In this heated environment, with frequent reports of immigrants tearfully torn from their families and deported, large segments of the population could refuse to participate in the census, out of fear the authorities could use the information against them, critics say.
In December, the Justice Department kicked up a storm when it asked to have a question on nationality added to the survey conducted by the Census Bureau, which is a part of the Commerce Department.
The Justice Department argued that citizenship information would help enforce the Voting Rights Act, however, that the law is aimed at prohibiting racial discrimination at the ballot box.
Only US citizens are allowed to register to vote. But Mr Trump has long claimed that millions of illegal immigrants voted in the 2016 presidential election, without providing proof.
"The Census Bureau is conducting a review of the DOJ request," said Mr Al Fontenot, associate director for Census programmes.
"We are focused on having the final list of questions submitted to the Congress by March 31st."
The debate over the questions and how they could affect response numbers is not just one of politics. Required by the Constitution, the census determines the number of seats allotted to each state in the House of Representatives, the lower chamber of the US legislature.
Stanford University sociology Professor C. Matthew Snipp said the survey is "essential for American democracy".
The population tally also impacts distribution of more than US$675 billion (S$891 billion) in annual federal funding for schools, hospitals, roads and public services, according to the Census Bureau.
Under-reporting in some communities is a longstanding problem. Analysts estimate that the 2010 Census undercounted Latinos by 775,000 people.
The problem could be worse this time.
If minority populations, often concentrated in Democratic-leaning urban centres, do not fully participate, this could affect the balance of power in Congress.
"States like Texas, California, Arizona that have large Hispanic populations could lose seats in Congress if there is a very large undercount," Prof Snipp said.
And NALEO's Mr Vargas warned that making a major last-minute change to the questionnaire would sabotage the Census Bureau's technical efforts to improve results and analysis.
Mr Vargas said an imprecise census also could have economic and financial impacts.
The change also could increase the cost, currently estimated at US$15.6 billion, up from US$12.9 billion in 2010, due in part to the need for follow-up visits to convince members of the public to respond.
And businesses use the decennial survey to identify demographic trends and locate consumers and potential employees, allowing them to tailor planned investments, plan for factories and retail outlets, and convince banks to provide financing.
In 2010, the Census counted 308.8 million Americans, an increase of 9.7 per cent from 2000. According to the latest estimates, the US population has since risen 5.8 per cent to 327 million.