The Queen is facing the prospect of the first ever industrial action by members of the royal household.

More than 100 low-paid staff at Windsor Castle are due to be balloted from Tuesday in a dispute about leading guided tours, the Public and Commercial Services union [PCS] said.

The announcement of the ballot came just before David Cameron’s meeting with the Queen about the official dissolution of parliament. A vote in favour would trigger members of the royal household taking industrial action just days before the general election.

The PCS claims staff have suffered years of pay restraint and are paid less than the living wage. PCS said new recruits at the castle start on as little as £14,400 a year.

The union, which represents 120 of the 200 staff at the castle, has proposed non-strike action that would involve the withdrawal of goodwill, such as giving tours of the castle to paying visitors.

The dispute concerns the payment of allowances for additional duties – mainly leading guided tours but including administering first aid and acting as translators. Last year, the staff accepted an “unsatisfactory pay offer” on the understanding that additional allowances for such duties would be considered this year. When these were refused, the union opted to ballot staff on industrial action. The vote closes on 14 April.

If staff vote in favour, industrial action would start before the end of April in the week before the general election. Windsor Castle said it did not anticipate disruption to visitors. It also claimed staff were paid above the market rate for Windsor and received additional perks including a free lunch.

The 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.”

A PCS spokesman said it was “coincidental” that the ballot was being held at the start of general election campaign. But he said the timing was “nonetheless welcome if it helps to put some added focus on how badly paid royal household staff are”.

Campaigners for an elected head of state accused the Queen of showing contempt for her staff. Graham Smith, chief executive of the Republic campaign, said:

“It is a failure of leadership on the part of the Queen that despite receiving close to £300m a year in public subsidy she continues to pay staff so badly.

“The Queen as head of state has a responsibility to set a higher standard, to lead by example. Paying hard-working staff such low wages while expecting them to do so much more than their jobs demand shows an appalling contempt.”

Smith added: “It is typical of the royals that they continue to demand more money for themselves, spending millions on refurbishing their homes yet they exploit the goodwill of those ordinary hard working people that keep the palaces running.”

He also called on the royal family to hand over the running of their palaces to the government, to give staff “the opportunity to call to account those who are paying them” and give them “a greater chance of demanding a fair, living wage”.

The Royal Collection Trust, the charity responsible for the Queen’s official residencies, insisted household staff could volunteer to lead guided tours but were not compelled to do so.

“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,” the statement said.

It added: “These are not compulsory aspects of their role, and it is the choice of the individual whether they wish to take part.”

It also claimed that staff wages were in line with government guidelines. It said: “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.”

It pointed out that the trust operated without public funding and added: “We don’t anticipate any interruption to the running of tours for visitors to the Castle.”

The PCS union responded by pointing out that wages at Windsor were failing to keep pace with the cost of living. A spokesman said: “The household has slipped behind the living wage because it hasn’t implemented the last uplift from November, and this will mean any new recruits and seasonal staff aren’t being paid it.

“The Royal Collection Trust should consider what message it sends to the world that staff who provide the public face of the royal family at Windsor start on just £14,400 a year.”