Beefeaters at the Tower of London took strike action on Friday for the first time in 55 years in a dispute over their pensions.

Visitors to the landmark were greeted by picket lines as jewel house wardens and other staff at some of the UK’s royal palaces staged a three-hour walkout.

The strike is the first by Beefeaters since 1963, when the Tower of London was closed during a series of Sunday strikes over a pay claim of 25 shillings a week, and a six-hour cut in their 48-hour week.

The Tower of London remained open on Friday, as did Kensington Palace and Hampton Court Palace, where three-hour walkouts were also taking place from 11.30am. Similar action is due to be repeated on 2 January.

About 120 staff, including a small number of Beefeaters, were taking part in the action over plans to move them from final salary pensions to a defined contribution scheme.

Facebook Twitter Pinterest Beefeaters chat to tourists at the Tower of London in 2017. Photograph: Neil Hall/Reuters

Members of the Public and Commercial Services Union (PCS) employed by the Historic Royal Palaces (HRP) charity voted heavily in favour of industrial action. The union’s general secretary, Mark Serwotka, said: “The unwarranted attack on our members’ pensions has forced them to vote for strike action.

“Our members are not paid a king’s ransom and the pension is one of the things that encourages people to stay in the job and deliver a first-class service to the public. People who treasure these historic buildings in London should be left in no doubt that any disruption caused due to strike action will be solely down to HRP’s intransigence in not paying our members a decent pension.”

HRP’s chief executive, John Barnes, described the industrial action as disappointing. “We have already offered substantial compensation and transition arrangements to the 11% of our staff who are affected,” he said. “The benefits they have already accrued will be fully protected, and they will be transferred onto the same competitive defined contribution scheme as the other 89% of their colleagues in April 2019.”

Beefeaters, the ceremonial guardians of the Tower of London, were formed by Henry VII in 1485 and were once responsible for guarding prisoners. Today they are confined to safeguarding the crown jewels and conducting guided tours. Their ranks are made up of 37 yeoman warders and one chief warder, all retired members of the armed services.

The origin of their nickname is uncertain. One theory is that it derives from the 17th-century slang term for the English, still in use in the French les rosbifs. Another is that it is a reference to their tradition of consuming rich and hearty beef broths known as “beffy”. A third is that they look similar to yeomen of the guard, a distinct corps of ceremonial bodyguards who were reputedly given a large daily ration of beef.