A former top adviser to Commerce Secretary Wilbur Ross told congressional investigators that he spoke to a professor who has advocated for adding a citizenship question to the 2020 census to limit the participation of illegal immigrants.

James Uthmeier appeared before the House Oversight Committee earlier this month but refused to answer more than 100 questions from panel staff on advice of Commerce Department lawyers, according to testimony released Tuesday.

The lawyers instructed Uthmeier not to discuss a secret memo he wrote about the citizenship question at the direction of Ross to John Gore, a Justice Department official.

“Despite these restrictions, Mr. Uthmeier provided the Committee with some new information,” a memo from Democratic members of the panel said.

He admitted that he sought advice about the question from John Baker, a Georgetown University law professor, who has argued that “the citizenship question is necessary to collect the data for a redistricting of House seats that excludes aliens from the calculation,” the memo said.

Ross, who oversees the Census Bureau, had said the request for the citizenship question had come “solely” from the Justice Department in 2017 as part of the Voting Rights Act to protect minority voting rights.

But documents and emails later revealed that Ross had been trying to get the question included months before that.

Democrats said it is an attempt to discourage the participation of minorities in the census that would lead to a redrawing of political maps in favor of Republicans.

“The Trump administration claimed that the only reason it wanted to add the citizenship question was to help the Department of Justice enforce the Voting Rights Act, but that claim has now been exposed as a pretext,” Rep. Elijah Cummings, chairman of the committee, said in a statement.

“Official after official appearing before the committee have refused to answer questions about the real reasons behind their effort​, but the mounting evidence points to a partisan and discriminatory effort to harm the interests of Democrats and nonwhites​,​”​ he added.

But a Commerce Department spokesman said the committee’s summary is not a transcript and “mischaracterizes” what Uthmeier said on “multiple topics.”

“In addition, Mr. Uthmeier, a former senior Department attorney, answered over 400 questions but declined, consistent with his ethical obligations, to discuss privileged communications. That was entirely appropriate,” the statement said.

Documents from a​ federal court case in Maryland also show that Republican strategist Thomas Hofeller, who died last year, recommended to Trump’s transition team that the question be added because it would benefit Republican candidates.

​A decision by the judge in the case said ​the evidence may warrant reopening a case claiming the question violates the rights of minorities.

​The Supreme Court is expected to rule this week whether the Trump administration can add ​the question to the census.