WASHINGTON — Trump administration witnesses were deliberately misleading when they testified about the origins of a plan to include a citizenship question on the coming census, opponents of the idea said Thursday, citing recently discovered evidence.

While the government has maintained that adding the question was intended to improve enforcement of the Voting Rights Act, the driving force was actually a desire to get more Republicans elected to state legislatures and the House of Representatives, the ACLU said in new court filings.

The Supreme Court is now considering whether the Commerce Department acted properly in ordering the Census Bureau to include a question about citizenship on the 2020 census form that goes to every U.S. household, despite warnings from populous states that doing so would actually make the count less accurate.

The case was argued April 23, but the ACLU on Thursday notified the court of the discovery.

Commerce Secretary Wilbur Ross told Congress that he ordered the question added after receiving a letter from a Justice Department official, John Gore, who said the data would improve administration of the Voting Rights Act. But the ACLU said Thursday that the suggestion for adding the question, and some of the actual language in that letter, came from a man with a long track record of helping get more Republicans elected by carefully drawing political district boundaries.

The ACLU told a federal judge in New York that the new evidence suggests Gore and an adviser to the Commerce Department "falsely testified about the genesis of DOJ's request." They wrote to Judge Jesse Furman, who in January ordered the government not to include the question. Though Furman's decision is now on appeal, he retains authority to discipline witnesses who did not testify truthfully, the ACLU said.

Furman scheduled a hearing for June 5 on the ACLU's motion to impose sanctions on the government witnesses. A Justice Department official said Thursday evening that the Department was unaware of the new evidence. "We intend to file a response in court," the official said.

The ACLU said the new evidence reveals that the idea originated with Thomas Hofeller, a Republican redistricting specialist, who wrote in letters and memos that the question would create an electoral advantage for "Republicans and Non-Hispanic Whites." He helped ghostwrite a draft of the Justice Department letter, which adopted his rationale and some of the actual wording, the ACLU said.

Getting better citizenship data, Hofeller argued in newly disclosed documents, would help Republican legislatures create legislative and congressional district maps with fewer Latinos, who tend to vote for Democrats.

"Witnesses misrepresented the origin and purpose of their effort to add a citizenship question to the census. Their goal was not to protect voting rights, but to dilute the voting power of minority communities," said Dale Ho of the ACLU, which represents the 18 states challenging the administration's plan.

Both the Trump administration and the challengers agree that adding the citizenship question will reduce the census response rate, especially in immigrant communities. But when the case was argued in April, the court's conservative majority seemed prepared to rule that Ross had acted within his authority to add it, because no method is guaranteed to produce an accurate count.

A census is required every 10 years by the Constitution, and the results determine how many members of Congress each state gets in the House of Representatives. The data is also used to calculate a local government's share of funds under many federal programs.