If an employer makes a mistake on a paycheck. Can they request repayment a year later?

In the majority of instances the employer can require repayment for any over payment without a time limit. This is true even if your employer is the one making the mistake on the calculation of the pay check. If you are working under a union contract, a written employment contract, or if your employee manual says different you may be able to avoid repayment. However, if you are an at will employee (not under any contract) your employer legally makes the rules. The best plan for an at will employee in this situation is to negotiate with the employer to repay the amount owed over a period of time, perhaps with payroll deductions. A word of caution here, there seems to be epidemic of employers who are just now auditing their books and finding discrepancies in payroll. Many of the employees who get stuck with the notice of repayment are outraged and are refusing to repay anything. At that point the at will employee is terminated for stealing. To make matters worse the employer then fights the employee getting unemployment benefits on the basis of stealing, and the employer wins. Some courts have said that every employee is responsible to look at their paycheck and to report discrepancies to the employer right away.