Staff at Windsor Castle in England earn less than the living wage and typically start at £14,400 per year ($21,260 USD). In addition to the duties for which they are hired, castle workers are expected to perform extra jobs like giving guided tours and interpreting - all without compensation, according to U.K.'s The Telegraph.

The Public and Commercial Services Union (PCS) represents 120 of the 200 staff at Windsor and maintains that promises have been broken by the royal household. The union ballot will take place between Tuesday, March 31 and April 14. Any industrial action will be taken at the end of April.

"These workers are loyal to their employer and absolutely committed to ensuring visitors are given the royal treatment," said Mark Serwotka, general secretary of the PCS, according to The Telegraph. "It is scandalous that staff are so appallingly paid and expected to do work for free that brings in money for the royal family."

The staff voting on industrial action are employees of the Royal Collection Trust. They are not employees of the royal household, like footmen and butlers would be. The workers willing to go out on strike are employees of the tourism aspect of the castle.

According to The Telegraph, the Royal Collection Trust said in a statement: "Warden staff are offered voluntary opportunities to receive training and develop skills to lead guided tours for visitors as part of their working day and to administer first aid, as well as to use their language skills.

"These are not compulsory aspects of their role, and it is the choice of the individual whether they wish to take part.

"Wardens at Windsor Castle are paid above market median based upon the Regional Living Wage and receive a range of benefits, including a 15% non-contributory pension and a free lunch.

"Royal Collection Trust continues to award wardens an annual performance-related pay increase of up to 2.5%, in addition to the cost of living increase (in line with treasury guidelines), as well as one-off payments to those who have reached the top of their pay scale.

"We don't anticipate any interruption to the running of tours for visitors to the Castle."

According to The Telegraph, Buckingham Palace refused to comment.