(CNN) House Ways and Means Committee Democrats are arguing that newly reviewed documents dating to the Nixon administration reveal that the law a congressional committee used to request President Donald Trump's tax returns has been used to request presidential tax information from the IRS before and that committee received it.

They cite newly surfaced documents that show that when the Joint Committee on Taxation undertook an investigation of former President Richard Nixon's tax returns that he turned over to Congress, there was tax information that was not covered in that voluntarily disclosure that the committee got directly from the IRS through 6103.

In response to a request from House Ways and Means Chair Richard Neal, Thomas Barthold -- the chief of staff of the Joint Committee on Taxation -- wrote that he had reviewed materials from the committee's files on Nixon.

"Based on this review, I can state that the Joint Committee staff sought and received, under its legal authority, confidential information directly from the Internal Revenue Service," Barthold wrote.

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