The investigators are probing whether Whitaker’s accepting of the donations, amounting to $8,800, violated the Hatch Act’s prohibitions on political activities by federal employees.

A spokesperson for the Office of Special Counsel confirmed to CNN that it had received a complaint from the watchdog organization American Oversight and a case file had been opened. The office has the power to investigate Hatch Act violations and determine possible reprimands, but cannot take disciplinary action itself, according to CNN.

“After years of being completely dormant and only after he joined Jeff Sessions’ office as chief of staff, Whitaker’s campaign started receiving a cluster of contributions,” Austin Evers, the executive director of American Oversight, told CNN. “It appears to violate the black-letter law of the Hatch Act.”