Another Boeing whistleblower has stepped forward, a Senate office announced hours before the company’s CEO is set to testify Tuesday in Washington for the first time since the door plug of a 737 Max 9 blew off during an Alaska Airlines flight in January.

Sen. Richard Blumenthal’s (D-Conn.) office identified the whistleblower as Sam Mohawk, a quality assurance inspector for the planemaker in Renton, Wash. Mohawk alleges Boeing improperly tracked and stored faulty parts, and that those parts were likely installed on airplanes including the 737 Max, which is manufactured at the Renton facility.

“Mohawk has also alleged that he has been told by his supervisors to conceal evidence from the FAA, and that he is being retaliated against as result,” according to a statement from the Senate Homeland Security’s Permanent Subcommittee on Investigations.