Members of the PCS who work at Windsor Castle are being balloted between March 31 and April 14 over whether they will take industrial action, which could affect tours of Windsor, one of the Queen's official residences, from the end of April – not long before the U.K.'s busy summer tourist season is about to start. The castle is the oldest and largest occupied castle in Europe, and is used as the Queen's weekend home.
Mark Serwotka, general secretary of the PCS, said: "These workers are loyal to their employer and absolutely committed to ensuring visitors are given the royal treatment.
"It is scandalous that staff are so appallingly paid and expected to do work for free that brings in money for the Royal Family."
- By CNBC's Catherine Boyle