GOP Rep. Nancy Mace is under investigation by the House Ethics Committee for allegedly attempting to profit off of a congressional program intended to defray housing costs for lawmakers’ Washington, DC, residences — a claim she has denied.

According to a newly published report from the Office of Congressional Conduct, the South Carolina Republican sought and was paid roughly $9,500 beyond the actual costs of her residence in DC.

“There is substantial reason to believe that Rep. Mace engaged in improper reimbursement practices,” the nonpartisan watchdog group said in its official referral to the House Ethics Committee. The ethics committee announced Monday it is investigating the matter.