WASHINGTON (Reuters) - The top U.S. law enforcement officer and the Commerce secretary will face a contempt of Congress vote unless they hand over documents by Thursday on efforts to put a citizenship question on the 2020 census, the chairman of a House of Representatives panel warned on Monday.

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Representative Elijah Cummings, chairman of the House Oversight and Reform Committee, sent letters to Attorney General William Barr and Commerce Secretary Wilbur Ross warning them they had until Thursday to comply with the subpoena after having failed for two months to produce the documents.

Barr also faces a contempt vote next week by the full House on whether he failed to comply with a subpoena seeking the full, unredacted report on Russian meddling in the 2016 election.

The House panel’s move comes as the Supreme Court is expected to soon render judgment on a lawsuit over the census issue.

The conservative-majority court appeared poised after arguments in late April to accept the administration’s position that the citizenship question would yield better data to enforce the Voting Rights Act, which protects eligible voters from discrimination.

But an immigrant advocacy group said in a filing in a Manhattan federal court last week that a longtime Republican specialist on drawing electoral districts played a “significant role” in planning the citizenship question.

The filing charged that the Trump administration had concealed evidence that its proposal for the question was intended to help Republicans draw favorable electoral maps during the next restricting based on the census.

A study by Harvard researchers in March predicted the citizenship question would lead to an undercount of some 4.2 million people among Hispanics, costing their communities federal aid and political representation.

The Commerce Department issued a statement accusing the House panel of using “mere insinuations and conspiracy theories” to “desperately and improperly influence the Supreme Court.”

It said the department had produced 14,000 pages of documents and Ross had testified nearly seven hours over the issue. The Justice Department did not immediately respond to a request for comment.

In his letter to Ross, Cummings said the Commerce secretary had testified he added the citizenship question solely at the request of the Justice Department to help enforce the Voting Rights Act.

“Last week, new documents were unearthed that suggest that the real reason the Trump administration sought to add the citizenship question was not to help enforce the Voting Rights Act at all, but rather to gerrymander congressional districts in overtly racist, partisan and unconstitutional ways,” he added.

Cummings said the panel would consider postponing its contempt of Congress vote if Ross and Barr produced unredacted documents the committee had requested by Thursday.