The House Oversight and Reform Committee is investigating allegations of voter suppression in Georgia under Secretary of State Brian Kemp, who has since become governor.

The investigation was revealed in letters that the committee’s Democratic leaders sent on Wednesday to Mr. Kemp and his successor as secretary of state, Brad Raffensperger. The letters instructed Mr. Kemp and Mr. Raffensperger — both Republicans — to provide by March 20 a wide range of documents concerning voter roll purges; holds placed on voter registration applications; polling site changes and closings; and other voting-related issues.

The committee also requested all documents related to the potential conflict of interest Mr. Kemp faced in administering an election in which he was a candidate.

“The Committee is particularly concerned by reports that Georgians faced unprecedented challenges with registering to vote and significant barriers to casting their votes during your tenure as secretary of state and during the 2018 election,” Representatives Elijah E. Cummings, the committee chairman, and Jamie Raskin, head of the Subcommittee on Civil Rights and Civil Liberties, wrote to Mr. Kemp.