Changing from Hourly to Salary?

Your question depends on why the employer changed you to salary from hourly, and whether your job is what is referred to as exempt (meaning you are not entitled to overtime) or non exempt.  If you are not in a supervisory or manager position, and do not work as a professional (e.g. accountant), then the employer is required to pay you overtime and cannot avoid that by paying you salary.  If you are an exempt employee, then the employer would be able to change your compensation to salary without any detailed explanation.  The change, however, can only be made prospective from the date he tells you this; he make the change retroactively