Retroactive Pay Deductions

My husband was hired by a large corporation to be the Manager of a new concept opening in another town. After training, he was informed that the new concept would not open for at least two years. They did not know what to do with him and for a while he was driving two hours a day to one of their restaurants, but they finally moved him closer to home. Unfortunately his new position was basically a demotion and he was forced to take a significant pay cut. I understand that they have the legal right to do this, even though it was not through any fault of his own, but here is the problem: They failed to change his wages for the first two months that he worked there, and because his check is automatically deposited, we didn't catch the mistake right away. When they caught it, about two days after we did, they informed him that they are taking ALL of the extra money out of his next paycheck, which means his next check will be about 1/4 of what he usually makes, if we are lucky. He asked them to take it out in installments, but they refused. Can they do this legally? We can't pay our bills this month, including our house payment, if they take it all out at once. Thanks for any advice.