The royal family faces industrial action by low paid staff in Windsor Castle as the PCS today opens a ballot over allowances.

It would be the first such action specific to the Royal Households and comes after years of pay restraint has left loyal workers paid below the widely-recognised Living Wage, with new recruits starting on as little as £14,400 a year.

Despite this, staff are expected to carry out extra unpaid duties, including giving tours of the castle – even though visitors are charged for these – and acting as language interpreters and first aiders.

The union, which represents 120 of the 200 staff at Windsor, says non-strike industrial action would involve withdrawal of this goodwill, and would have a significant impact on the services provided to visitors.

An unsatisfactory pay offer for 2014 was only narrowly accepted by staff on the understanding that the additional allowances would be considered this year.

But senior officials in the Royal Households have again refused to reward staff for their goodwill and pay allowances for additional duties.

The ballot opens today and closes on 14 April, with industrial action planned to start from the end of the month.

PCS general secretary Mark Serwotka 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.”