In short, no it's not legal. In general, if you were an at-will employee, you are free to quit at any time and are entitled to the wages and benefits you already earned at the agreed upon rate. Therefore, absent some employment contract, a prior notice that your wages were going to be reduced, or some faithless conduct on your part, you should be entitled to the full amount of wages that you earned prior to the time you quit. Of course, the specific facts need to be considered and various state or federal laws may be involved, so you should consult an employment attorney if you are in fact paid at a reduced rate. Best of luck.
Cornetet, Meyer, Rush & Kirzner
No attorney-client relationship implied or accepted without a signed fee agreement. This response is theoretical only and for purposes of discussion. Attorney is not liable for any opinion expressed herein. Attorney is licensed in Ohio only.