A pay strike by civilian workers at a number of RAF stations, including in Shropshire, will go ahead after last-ditch peace talks broke down.
More than 200 cleaners, chefs, drivers and other employees at eight sites in England and Wales will walk out on Thursday, with further stoppages expected.
Members of the GMB and Unite unions are in dispute with contractor ISS after saying they had been offered a pay rise of 8p an hour, and only 2p for those on the national minimum wage.
The sites include Valley in Anglesey, North Wales, where the Duke of Cambridge is based as a search and rescue helicopter pilot.
Other bases affected by the strike are Cranwell, Scampton and Kirton-in-Lindsey in Lincolnshire, Shawbury and Cosford in Shropshire, Llanwrst in Conwy and Fairbourne in Gwynedd.
GMB official Sian McClarence said: "For nearly six months, ISS have been sleep-walking into a dispute at the RAF."
Unions claimed that military personnel from other sites will be drafted in to cover for the striking workers.