In the United Kingdom, under the National Minimum Wage Act 1998, workers operating under a zero-hour contract on stand-by time, on-call time, and downtime must be paid the national minimum wage for hours worked. Prior to the introduction of the Working Time Regulations 1998 and the National Minimum Wage Regulations 1999 zero-hour contracts were sometimes used to "clock-off" staff during quiet periods while retaining them on site so they could be returned to paid work should the need arise. The National Minimum Wage Regulations require that employers pay the national minimum wage for the time workers are required to be at the workplace even if there is no "work" to do. In the past, some employees working on a zero-hour contract have been told that they are required to obtain permission of their employer before accepting other work but this practice has now been banned under UK legislation enacted in May 2015.