I am not sure what sort of personal financial information and what type of establishment this is, but ultimately this could at the very least be considered an invasion of privacy. If you would expect a reasonable expectation of privacy in your personal financial information and this has nothing to do with your work with clients or customers, then this person is violating the law pure and simple and not only could it be a civil litigation matter but it could violate several labor laws, including workplace harassment and creating a hostile working condition. If you have proof of what this person is doing and may have the consumers on your side, I say contact the state labor department and also a private attorney. If this is a chain, contact corporate. You cannot be fired in retaliation and further many states have good whistleblower statutes that may apply.