A union representing Boeing employees said this week that the plane maker, in 2022, retaliated against two engineers monitoring its safety practices on behalf of the Federal Aviation Administration (FAA).

The Society of Professional Engineering Employees in Aerospace (SPEEA) filed a complaint to the National Labor Relations Board on April 18 saying Boeing gave the two employees “identical” negative performance evaluations—a crucial metric that determines raises, promotions, and layoffs.

The two engineers were Boeing employees and also reported to the FAA through the agency’s Organization Delegation Authorization program, a status that gave them workers oversight of Boeing’s safety practices. SPEEA’s Tuesday statement said the employees were reluctant to use Boeing’s “Speak Up” protocols after identifying quality concerns out of fear that their supervisors would not listen. The engineers fought with supervisors for six months over company practices, which eventually led to a re-evaluation of the company’s engineering work.

“We have zero tolerance for retaliation and encourage our employees to speak up when they see an issue,” Boeing told Fortune in a statement. “After an extensive review of documentation and interviewing more than a dozen witnesses, our investigators found no evidence of retaliation or interference. We have determined the allegations are unsubstantiated.”

SPEEA executive director Ray Goforth said he doesn’t buy Boeing’s claims.

“If Boeing is so confident in the quality of that investigation, why is it hiding the report to the FAA? Under federal law, Boeing is required to share that report with SPEEA, and it refuses to do so,” he told Fortune in a statement. “Boeing has forfeited the right to be taken at its word by anyone.”

SPEEA’s statement and the release of the complaint came just hours before Boeing reported its first quarter earnings. While the company had a better-than-expected outcome, it still posted a $355 million net loss—largely a result of the fallout of the grounded Jan 5. Alaska Airlines flight, which triggered increased FAA scrutiny. Following the FAA’s investigation in March, which found more than a dozen operational problems with Boeing’s aircrafts, the regulatory body is requiring the manufacturer to report on its revamped safety and quality procedures on May 28. 

Mounting concerns

SPEEA’s complaint was filed the day after whistleblowers and industry experts testified about Boeing’s safety culture in front of the Homeland and Governmental Affairs Senate subcommittee led by Democratic Sen. Richard Blumenthal of Connecticut.

During the hearing, Boeing quality engineer and whistleblower Sam Salehpour, who has worked for the company for 30 years and is still an employee, said he raised concerns to supervisors about the quality of Boeing’s aircrafts over the course of three years. Salepour came forward earlier this month, saying that about 1,400 787 and 777 Max models were flying with potentially serious structural weaknesses and were at risk of premature failure. He said his concerns fell on deaf ears within the company.

“I was ignored. I was told not to create delays,” he said during the hearing. “I was told, frankly, to shut up.” 

Salehpour told the subcommittee that after working in the company’s 787 division as an engineer, he was moved to the 777 division because of his repeated comments questioning the safety of gaps between aircraft panels. He said his supervisor stopped inviting him to meetings and was then offered a “new job” in the other department.

“They do it pretty stealthily,” he said.

Other Boeing whistleblowers includeJohn Barnett, who criticized the company’s allegedly shoddy practices in its North Charleston, S.C., facility in 2019 following two plane crashes that killed 346 passengers. He died by suicide in March, hours after he testified before the Department of Labor’s Office of Administrative Law Judges. 

Barnett said that in 2015, after he warned his supervisor of a manufacturing error that could cause short-circuiting, his boss relegated him to the “materials review segregation area” of the facility, a move Barnett considered not only retaliation, but basically a demotion.

“You want to be touching the airplane, that’s a great job,” he said. “Going to be the manager of a parts store, that’s pretty humiliating.”