Nancy Mace, a Republican representative, is under investigation by the House ethics committee over allegations that she may have improperly claimed more than $9,000 in reimbursements meant to subsidize housing costs for members of Congress.

According to a report from the nonpartisan Office of Congressional Conduct (OCC), which reviews ethics complaints against lawmakers, the South Carolina representative’s requests for reimbursement had exceeded the total of her DC property expenses during several months in 2023 and 2024, “amounting to an excess of $9,485.46.”

The OCC said in its referral to the House ethics committee that there is “substantial reason to believe” that she had “engaged in improper reimbursement practices”.

Mace was participating in a federal program that is intended to help subsidize lodging, food and travel expenses for lawmakers who must maintain households both in Washington DC and in their districts.

The report said she consistently “requested and received the maximum allowable reimbursement”, and the OCC’s review of invoices, utility bills and other documents “identified discrepancies between the amounts requested and received by Rep Mace … and the total of these associated bills”.

According to the report, the finding of over $9,000 in excess reimbursements is based on the assumption that Mace was responsible for 100% of the property costs despite her only having a 28% ownership stake.

According to the OCC report, Mace did not respond to their inquiries and declined to be interviewed for their review. “Because Rep Mace declined to interview with the OCC in this review, the OCC was unable to confirm the extent of Rep Mace’s financial obligations with respect to the DC Property,” the report said.

The Guardian reached out to Mace’s office for comment.

In a statement to Politico, her office accused the OCC of being a partisan office that “retaliates against women and ignores its own evidentiary standards”. Mace said in a post on X on Monday that she is “not taking seriously” the ethics complaint.

An attorney for her, William Sullivan, disputed the claims in a letter to the House ethics panel, calling the OCC report “fundamentally flawed”. Sullivan suggested that the report’s “narrative appears to incorporate unverified assertions and materials that may have originated from, or been influenced by, Rep Mace’s former fiance,” Patrick Bryant, who co-owned the property with her.

Mace publicly accused Bryant and three other men of sexual misconduct during a House subcommittee hearing last February. Bryant has denied those allegations and filed a defamation suit against Mace.

“Rep Mace is confident that the committee will carefully evaluate the origins and credibility of the information at issue and will recognize the significant deficiencies that undermine” the report, Sullivan wrote.

Mace is not seeking reelection to the House. Instead she is running for the Republican nomination for governor of South Carolina, which is holding its primary on 9 June. The allegations will no doubt add further turmoil to her bid for governor after she reportedly berated staff at Charleston international airport, which she has denied.