CNN  —  A union representing Boeing engineers has alleged the plane maker retaliated against two employees who, at the time, were working on behalf of the Federal Aviation Administration (FAA) to provide manufacturing oversight. The allegations came to light in recent days after the Society of Professional Engineering Employees in Aerospace (SPEEA) filed a complaint with the National Labor Relations Board on behalf of one of the two engineers seeking to uncover a report from Boeing’s (BA) internal investigation into the incident which was filed with the FAA. The complaint and a press release issued Tuesday by the union describe how the two workers “insisted the company reevaluate prior engineering work on the 777 and 787 to account for a new FAA advisory” in 2022. SPEEA says Boeing initially pushed back against redoing the work before agreeing to do it, but then allegedly retaliated against the two in their performance reviews. The union says it is trying to appeal a decision not to change the performance evaluation of one of the workers. It said in the press release that “the other (worker) has quit Boeing over the way he was treated.” The complaint, dated April 18, says “these two employees received (identically) downgraded marks on the ‘Performance Values’” part of a performance review after raising their concerns. It goes on to say that one of the employees then “filed a ‘Speak Up Report’ to challenge this apparent retaliation.” Boeing then investigated the incident, but the union says the company would not provide it with a copy of the report. Boeing says the investigation was part of a confidential process and that the report could only be shared with the FAA. “We have zero tolerance for retaliation and encourage our employees to speak up when they see an issue. 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,” Boeing said in a statement. The FAA says it is investigating the situation. Last week, a Boeing whistleblower, Sam Salehpour, told congress he has concerns about the way Boeing has been fusing together its fuselages on the 787 and 777 and that he faced retaliation after raising the concerns. The complaint filed on behalf of the two engineers involves a different issue— the onboard computer networks on the planes. The union says Boeing managers “strongly objected” to rerunning calculations regarding the systems based on new assumptions, citing cost and production delays, but that Boeing ultimately agreed. “After nearly six months of debate, the two engineers, with backing from the FAA, prevailed. Boeing re-did the required analysis,” the press release says. The union says the negative performance reviews could harm the engineers when it comes to promotions or could subject them to layoffs. “Even after the manager of the two engineers admitted that he had rated them both poorly at the request of the 777 and 787 managers who had been forced to resubmit their work, Boeing refused to change the engineers’ performance evaluations,” the press release says. “Whether it’s capital R ‘Retaliation’ or not, the fact remains that the two ODA designated SPEEA members did the right thing and stuck to their guns despite heavy pressure from Boeing, and then got hit with career-damaging performance reviews. This helps show why Boeing doesn’t have a healthy safety culture,” SPEEA Director of Strategic Development Rich Plunkett said in the release.