Aramark employee Jon Costa says he brought up his concerns to upper management about food safety before the World Series. (6:55)

The food safety manager who went public last fall with allegations of unsafe food handling and pictures of bugs, mouse feces and moldy food at Kansas City's Kauffman and Arrowhead stadiums has been fired.

Jon Costa shared with "Outside the Lines" a copy of a letter he said his former employer, Aramark, sent him on March 17 saying Costa was being fired "for cause." The letter outlines a number of reasons, the first of which is that he violated the company's media policy by taking his concerns public.

Costa came forward publicly with his concerns last November, just after World Series games at Kauffman Stadium, in an email to media and public health officials, including the local health department. He detailed allegations -- complete with photos -- of cockroaches in vending areas, mouse feces on the same tray as pizza dough, sinks where employees were supposed to wash their hands being blocked by boxes or trash, employees eating in food prep areas and trays of food headed for customers that measured at unsafe temperatures.

The city health department responded with an inspection of the Royals' and Chiefs' stadiums on Nov. 3 that found violations at 20 out of 26 stands, including 37 critical violations, including mold growth in ice machines, dirty pans and trays and excessive numbers of fruit flies. A subsequent inspection found those violations to be corrected.

Aramark declined to answer specific questions about Costa's firing but issued a statement Thursday noting that "We respect our employees' privacy and consider personnel matters confidential. We maintain that privacy even if an individual chooses to discuss their situation publicly."

The company defended its food safety record: "In Kansas City, we have served over 17 million fans since 2007 at hundreds of games and events and have a strong record of performance. We have continued to work closely with the Kansas City Health Department who has inspected Truman Sports Complex more than 100 times over our operating tenure. None of our Kansas City sports operations have ever been shut down by the Health Department and there have been no cases of food-related illness tied to our operations."

Expired pizza dough was served at Kauffman Stadium for Game 7 of the World Series, a food manager at the stadium told "Outside the Lines." Courtesy of Jon Costa

Aramark put Costa on paid administrative leave on Nov. 5, 2014. On Nov. 18, Costa's attorney said he requested that Aramark reinstate Costa. Costa questions the timing of his firing, noting that the Royals' home opener is April 6.

"I honestly would have gone back to work and be reinstated," Costa said. "I knew it would have been a very hostile environment, but there would have been a ton of things to fix there. But I was up to the task."

An Aramark representative interviewed Costa on three separate occasions after the November publicity, during which Costa said he was asked questions about his employment, prior work history, the nature of his photos and other aspects of his allegations.

In December, Costa's attorney filed a retaliation complaint with the U.S. Occupational Safety and Health Administration, which has the authority to investigate complaints of retaliation against whistleblowers.

In its letter of termination, Aramark also said Costa "failed to take prompt action to address food safety issues, notwithstanding documented support from his managers and direction from them to do so" and to discipline employees who were violating food safety practices.

But Costa said he had tried to solve problems by addressing them on site and bringing them to the attention of managers who never supported his efforts. He said he did not supervise anyone and had neither the authority nor training to discipline fellow employees.

The letter detailing his firing also says that Costa hampered Aramark's relationship with the local health department and that he did not follow protocol in dealing with the department. Costa, who used to work for the City of Kansas City, Missouri, Health Department, denied those allegations. When "Outside the Lines" interviewed health department division manager Naser Jouhari in November, he said he knew Costa as a former employee and Aramark representative and that, "It's all been pleasant. We never had any major concerns."

Costa's attorney Ryan McClelland, who specializes in employment law, said he believes that Aramark fired Costa not for going to the media but for alerting public health officials of the violations.

"Jon, making a good faith reporting of food safety violations, is a protected activity for which he can't be subject to any adverse action," McClelland said.

McClelland said the firing was especially retaliatory in part because the company denied Costa ongoing medical coverage, which usually happens only in cases of "gross misconduct." Although Missouri doesn't have protections for whistleblowers in the private sector, McClelland said Costa's issue could still fall under state wrongful termination laws as well as a variety of federal statutes, including through OSHA. An OSHA official stated that the agency tries to complete its investigations within six months.