An employee at a chemical company noticed that several of the security personnel at the company allowed tankers to be filled over the legal limit with highly flammable gases. The employee gathered evidence of such instances and presented it to senior management. A few months later, the company had not acted, and the employee contacted the Occupational Safety and Health Administration. Less than a week later, the company fired him. Assuming that the employee had not had disciplinary issues and wanted to file a claim alleging he was wrongfully discharged, what would be the strongest basis for his claim