The US supreme court on Friday rejected a request by Donald Trump’s administration to halt a trial set to begin on Monday that will test the legality of the government’s contentious decision to ask people taking part in the 2020 national census whether they are citizens.

The administration had argued that there should be no trial in the legal challenge brought by 18 states to the citizenship question until the justices rule on a fight over evidence. That dispute includes whether the commerce secretary, Wilbur Ross, whose department oversees the US Census Bureau, should be forced to answer questions under oath about his motivations for the politically charged decision.

An indefinite postponement of the trial, as sought by the administration, could have made it impossible to resolve the dispute before census forms are printed starting next year.

In March, New York led a coalition of Democratic states in a lawsuit against the Trump administration over a decision to include the citizenship question on the 2020 census.

The census is carried out every 10 years and helps to determine political representation in Congress, federal funding of programs and other matters.

The US Department of Commerce had said in a press release at the time that citizenship data would help the Department of Justice enforce the Voting Rights Act, which protects minority voting rights.

In February, a coalition of state attorneys general had urged the commerce department not to add such a question, saying it could lower participation among immigrants and cause a population undercount.

New York’s then state attorney general, Eric Schneiderman, said the question asking residents about their citizenship status would create fear and mistrust in immigrant communities and could skew census results if some immigrants choose not to participate.