Whistleblowers can expose a variety of illegal actions at the employer level, but these claims tend to center upon issues such as tax fraud, accounting fraud, employment discrimination, fraud in the healthcare system, violations of wage and hour laws, failure to pay overtime and more.  Importantly, whistleblower protections apply in any case where you reasonably believed that your employer was committing some type of illegal action or violating public policy to protect you from retaliation and adverse employment actions.