The American Civil Liberties Union and other lawyers asked the Supreme Court on Wednesday evening to consider putting off a decision on whether to allow a citizenship question on the 2020 census and allow a lower court to gather more information about the role a prominent Republican redistricting expert played in getting the question on the survey.

The Supreme Court heard oral argument in the case in April, and a decision is expected by the end of the month, possibly as soon as Monday. The timing of the request is unusual: Filings at the Supreme Court usually cease after oral arguments, and a decision is expected in the next two weeks. The U.S. Census Bureau has said it needs a decision by the end of June because it needs to send the forms to be printed no later than July 1.

The filing comes after lawyers for the ACLU and Arnold & Porter, who are representing advocacy groups challenging the question, obtained files belonging to Thomas Hofeller, a Republican redistricting expert who died in August. The lawyers say the files prove Hofeller played a role in adding the citizenship question because he had drafts of language that was ultimately used to add it. The lawyers also discovered a 2015 study that Hofeller authored arguing that adding a citizenship question to the census was a crucial step to pave the way for redistricting that benefits whites and Republicans.

In their filing Wednesday, the ACLU and Arnold & Porter lawyers urged the Supreme Court to uphold a lower court ruling blocking the citizenship question from the census. But if the justices consider not upholding that ruling, the lawyers asked them to put off a decision and send it back to the lower court so they can further explore Hofeller’s role. U.S. District Judge Jesse Furman, who initially struck down the question, declined last week to order more discovery about Hofeller’s role in adding the question until the Supreme Court had ruled.

“The Court should not bless the Secretary’s decision [to add the question] without answers to outstanding questions going to the heart of the case,” the lawyers wrote. “If ever there were a case that should be decided on the basis of a true and complete record, it is this one. The Decennial Census is one of the United States government’s most important constitutional responsibilities, and even an appearance that the government has manipulated the census for partisan and racially discriminatory purposes would undermine public confidence in our representative democracy.”

In their filing, lawyers for the challengers, who supported an expedited briefing in the case, cited testimony from a government witness in the trial suggesting the forms could be printed as late as October if the Census Bureau received additional funding.