By Ariane de Vogue, CNN Supreme Court Reporter

The American Civil Liberties Union late Wednesday night asked the Supreme Court to wait until the fall to decide if it wants to allow the Trump administration to add a question about citizenship to the 2020 census.

In a motion sent to the court, the group suggested that the justices send the case to a lower court to consider newly discovered evidence suggesting the question was added for political purposes.

A Census Bureau official testified during trial that the questionnaire could be printed as late as October 31, meaning there would be time to review the new evidence on an expedited basis, said Dale Ho, the director of the ACLU's Voting Rights Project.

"The census happens once a decade and there is no chance for a do-over," Ho said in a statement. "The Supreme Court should not permit the Trump administration to add a citizenship question to the census based on an incomplete and misleading record."

The eleventh-hour filing came the same day as the House Oversight Committee voted to hold Attorney General William Barr and Commerce Secretary Wilbur Ross in contempt for not complying with subpoenas for documents on the citizenship question and the White House asserted executive privilege for those materials.

The Supreme Court is wrapping up its term and will issue an opinion in the case -- one of the most significant on the docket -- by the end of the month. The justices do not have to respond to the motion until they issue a final opinion.

At oral arguments in April, it appeared that the conservative justices were inclined to side with the administration, although it's a tricky endeavor to try to ascertain how a case will come out based on what the justices say from the bench.

President Donald Trump defended the addition of a citizenship question on Wednesday, telling reporters in the Oval Office, "it's totally ridiculous that we would have a census without asking."

Evidence from deceased GOP operative

It was only earlier this month that the ACLU and a team of lawyers at Arnold & Porter said that they had obtained a trove of documents from a deceased Republican redistricting expert who, they allege, played a significant role in the decision to add the question. The expert, Dr. Thomas Hofeller, wrote a study in 2015 concluding that using "citizen voting age" population as the redistricting population base would be "advantageous to Republicans and Non-Hispanic Whites."

The administration has always denied political motivation, saying instead that the Justice Department had determined that the question was necessary to better comply with federal voting rights law.

The ACLU raced back to Judge Jesse Furman of the US District Court for the Southern District of New York, who ruled against the administration in January. At a hearing last week, Furman called the new evidence "serious" but said he didn't want to interfere with the case before the Supreme Court. He ordered lawyers to submit additional briefs in early July to consider sanctions against the government.

In its filing Wednesday, the ACLU writes that "the new evidence strongly suggests that Commerce's real rationale was the diametric opposite of its stated reason: not to protect minority voting rights through better enforcement of the (Voting Rights Act), but to facilitate a partisan advantage in redistricting and to dilute the electoral influence of voters of color."

The Justice Department has been deeply critical of the ACLU's allegations.

In a fiery letter to Furman last week, the Justice Department said Hofeller's work did not play "any role whatsoever" in the department's request to add the question.

"There is no smoking gun here; only smoke and mirrors," the Justice Department said, adding that a top department official had given testimony that was "entirely truthful."

"Substantively, the 'new' evidence is irrelevant because the critical" issue in the case "is whether (Ross) provided an objectively rational basis for his decision to reinstate the citizenship question," the department added. "Nothing in the private files of a deceased political operative can affect the resolution of that issue."