Immigrant-rights groups asked the Supreme Court on Wednesday to postpone ruling on their legal challenge to the addition of a citizenship question to the 2020 census until allegations that the query was intended to bolster Republican political advantages can be heard by a lower court.

The administration has said it added the citizenship question to improve enforcement of the Voting Rights Act of 1965, enacted to protect minority voters from discrimination.

The American Civil Liberties Union, which represents some of the challengers, has said that is a pretext, and its motion points to recently discovered evidence from a North Carolina redistricting case that it says shows the citizenship question originated with a Republican strategist who wrote that it could be “advantageous to Republicans and Non-Hispanic Whites.”

Three federal district courts this year have ordered the citizenship question struck after finding that the Commerce Department, which oversees the census, skirted federal law requiring transparency and reasonable grounds for policy shifts. The government appealed to the Supreme Court, which is expected to decide the case before month’s end.

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“The census happens once a decade, and there is no chance for a do-over,” said Dale Ho, an ACLU lawyer who argued before the justices in April. “The Supreme Court should not permit the Trump administration to add a citizenship question to the census based on an incomplete and misleading record.”

A Justice Department spokeswoman declined to comment on Wednesday’s filing. The department previously denied the ACLU allegations, dismissing them as “an unfortunate last-ditch effort to derail the Supreme Court’s consideration of this case.”

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While time is running out to prepare the census forms, the ACLU said the decennial count could proceed on schedule as long as the issue was resolved by October.

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