Historic Royal Palaces staff including Beefeaters and Jewel House Wardens could go on strike over proposed closure of their final salary pension scheme.
Sites including the Tower of London, Hampton Court Palace and Kensington Palace could be affected by a staff walkout if members of the GMB Union vote to take strike action over the proposed scheme closure.
The ballot, set to take place on Friday 30 November, comes as HRP has decided to close its final salary pension scheme to new entrants as of 1 April 2019.
The GMB says staff were promised pension continuity when their benefits were transferred from the civil service to Historic Royal Palaces (HRP).
The scheme was closed to new members in 2002. But now the final 120 remaining members face having their defined benefit pots closed, and contributions going forward put into less-lucrative defined contribution (DC) pension pots.
Mick Ainsley, GMB Regional Officer says: "They see their defined benefit (DB) pension entitlement as a critical element of the employment package, and quite rightly put a great value on it.
"HRP’s decision to close the scheme came as a great surprise. Difficulties or the ability to afford the pension had never been mooted before and members just see this attack on their standard of living for the rest of their lives.
Mr Ainsley accuses HRP of “jumping on the band wagon” as other firms close expensive-to-maintain final salary schemes.
He adds: "GMB members have made it very clear that they want more negotiations and are prepared to talk. Strike action is the last thing they want to do, but HRP have left them with nowhere else to go.
John Barnes, chief executive, Historic Royal Palaces responds: "In April 2019, we will be closing our Defined Benefit Pension scheme, affecting 11% of our staff. The scheme has become financially unsustainable, and the rising costs pose too great a risk for Historic Royal Palaces.
"We need to act in the best interests of the charity and of the majority of our staff, who will all benefit from a 2% increase in employer contributions to their pensions from April 2019 as part of the changes.
"This is not a decision we have taken lightly and we have consulted extensively with the staff affected over the course of the past year, as a result of which they will be receiving compensation and transition arrangements among the best in the market. They will be joining the same competitive Defined Contribution scheme as their colleagues.
"The Trade Unions will shortly ballot their members and we will await the outcome of this."
Complicated royal structure
Historic Royal Palaces was initially an agency of the old Department of the Environment, but became an independent charity in 1998 and manages unoccupied royal palaces on behalf of the Queen.
Mr Ainsley explains: "Currently, government responsibility rests with the Secretary of State for Culture, Media & Sport but all the palaces in HRP care are owned by the Queen 'in Right of Crown'.
“This means that the Queen holds the palaces in trust for the next monarch and by law cannot sell, lease or otherwise dispose of any interest in the palaces.”
Palaces such as Buckingham Palace and Windsor Castle, which maintain an active royal presence are managed separately.