EPA Administrator Scott Pruitt is under investigation for retaliating against employees who questioned his spending and management habits, according to a Sunday Politico report.

The U.S. Office of Special Counsel is reportedly reviewing claims from at least six current and former employees who were moved to different positions, took temporary leave, or were fired after pushing back against Pruitt on issues including his 24-hour security detail which has so far cost taxpayers $4.6 million.

The probe is one of around a dozen centered on Pruitt’s actions as head of the EPA.

A person who lodged one of the complaints and wished to remain anonymous told Politico that the allegations have credence. “These are highly educated, professional people who don’t complain. They do their job, they do it well and they’re tired of being abused by career employees who enable [Chief of Staff] Ryan Jackson and Scott Pruitt to get away with what they’re doing,” the source said.