You may not have to pay employees for every task they perform while getting ready to start their shifts. But if those employees can prove you told them they would be paid for that time, you may be liable.
Recent case: A group of FedEx employees sued, alleging the company told them they would be paid from the moment they punched in on the time clock until they clocked out at the end of their shifts. In reality, their paid time began when they first activated their portable task scanners. FedEx said its practices were legal under the Fair Labor Standards Act, but the employees insisted the company had promised to pay them.
The court sent the case to trial. The employees will have to prove the company led them to believe they would be paid from clock-in to clock-out. (Masterson v. FedEx, No. 07-CV-2241, MD PA, 2008)