They cannot garnish your wages without a court judgment or order in their favor. But if you were paid when you should have have been, they can:1) Sue you for the money, and if you were not suposed to be paid, they will win--the law is very clear that a mistake does not let you keep money to which you are not otherwise entitled. So they can get a court judgment ordering you to pay; if you don't, then they could garnish your wages.2) Fire you for refusing to repay money to which you are not entitled.So you very much want to work out a payment plan with them, sinc if you don't, the consequences could be worse.