If your employer wants to cut your hours to less than 40 per week, unless you have an employment contract or union agreement to the contrary, it is legal. Also, your treatment must not be due to some form of legally actionable disicrimnation. Otherwise, as an "at will" worker, your company can set the conditions of your employment much as it sees fit. That having been said, you have the right to quit, with or without notice. On the other hand, if your employer is not cutting your hours but labeling you as "part-time", you may have rights. As a general rule, most employers consider 40 hours or more to be full-time employment and anything less part-time. Federal law defines a part-time employee as someone who works less than 1,000 hours per year for the same company (17.5 hours per week). However, the laws about how many hours constitutes full/part-time employment can differ from federal law and can be determined state-by-state. You can check with your state department of labor to be certain of the law and/or consult directly with an employment law attorney.