A former manager at California’s San Onofre nuclear plant is suing his ex-employer, charging that the company wrongfully terminated him in retaliation for his efforts to blow the whistle on safety violations.

As Reuters reports, the firing came after the federal Nuclear Regulatory Commission sent a warning letter in March, 2010, to Southern California Edison, the principal owner of the San Onofre plant. It rebuked the utility for a workplace climate that, the agency said, had the “chilling effect” of preventing employees from raising safety concerns.

Paul Diaz, the plaintiff in the whistleblower case, said he was recruited, after a previous stint with the utility, to return early last year as manager of business, accounting and project service. According to his lawyer, he quickly clashed with his superiors.

“Some employees came to him with issues they were afraid to bring up because they feared retaliation, so he brought them up,” attorney Maria Severin said.

The lawyer said Diaz’s supervisors tried to dissuade him from airing safety issues. “They told him: ‘Don’t be a superhero,'” she said.

In October, Diaz, 35, was fired.

According to the lawsuit, Southern California Edison was warned by nuclear regulators in the March, 2010, letter as a result of anonymous complaints sent via email about safety shortcuts, incomplete testing, falsified records and “a culture of cover-up.” The lawsuit, which seeks unspecified damages, also says that the long hours and frequent demands for overtime led to frequent employee fatigue.

The company issued a statement saying that officials had not yet received the lawsuit and would not comment on its allegations. “However, we can say that, by policy, SCE considers retaliation against employees who raise safety concerns a termination offense,” the statement said.

The San Onofre facility, one of California’s two nuclear power plants, is located along the Pacific in northern San Diego County, about 60 miles south of Los Angeles.