Britain’s Queen Elizabeth is facing the first ever strike threat by her staff when workers at Windsor Castle vote over “appalling” low pay and allowances.

Castle staff start on as little as 14,400 pounds per year, meaning they earn less than the living wage, but are expected to carry out extra duties for no extra pay, such as giving guided tours to paying visitors and acting as interpreters and first-aiders, the Telegraph reported.

The Public and Commercial Services (PCS) Union, which represents 120 of the 200 staff at Windsor, said the Royal household has broken promises over giving the staff extra allowances for carrying out the extra duties.

The union will ballot its members between March 31 and April 14.

All the workers involved are uniformed wardens, who work in the corridors and rooms open to the public, protecting the exhibits and helping the public, as well as working in the ticket office, cloakroom and catering outlets.

“These workers are loyal to their employer and absolutely committed to ensuring visitors are given the royal treatment,” PCS general secretary Mark Serwotka said.

“It is scandalous that staff are so appallingly paid and expected to do work for free that brings in money for the royal family,” he added.

Windsor Castle, the largest and oldest occupied castle in the world, attracts 1.1 million visitors, who between them spend more than 17 million pounds (approximately $25 million), each year.

The money is used by the Royal Collection Trust charity for the upkeep of the royal palaces and their contents.