The controversial question of whether the Trump administration can add a citizenship question to the decennial census for the first time since 1950 came under scrutiny in recent weeks after newly surfaced documents suggested the proposed addition was politically motivated.

In a letter to a federal court in New York, civil rights groups pointed to a 2015 study written by Republican strategist Thomas Hofeller, which said a citizenship question would be advantageous to “Republicans and Non-Hispanic Whites”. 

The case was referred to the Supreme Court after two federal judges ruled against the inclusion of the question.

The Supreme Court is set to make a decision within the next few days as its current term is expected to conclude by the end of June.

Asking a question on citizenship is opposed by human rights organisations as well as various industry organisations and businesses, including the Insights Association and Nielsen. Critics say the question would hit response rates, leading to inaccurate data and ultimately flawed federal funding decisions over the next 10 years.

Meanwhile, a coalition of 125 business, local government and civic organisations have written to members of the House of Representatives to urge it to commit the full funding required as the census bill goes through the appropriations process.

The Commerce, Justice, Science and Related Agencies appropriations act has proposed $8.45bn for the Census Bureau, including $7.5bn for the census.

In a letter sent to every House member, the groups wrote: “An underfunded census would jeopardise the availability and validity of data used to make essential economic, political, and planning decisions in the nation’s private, public, and non-profit sectors over the next decade. To this end, we urge the House of Representatives to ensure a 2020 census that is equally successful in all communities by supporting the proposed Census Bureau funding level in the FY 2020 CJS bill, and by working to enact a final bill by the start of the fiscal year.”

Mary Jo Hoeksema, co-director of the Census Project, said: “Our coalition of census experts is gravely concerned about the risks to a successful 2020 count. Insufficient, delayed, or uncertain full-year funding for the 2020 census jeopardises the agency’s ability to meet its constitutional mandate.”