Seafarers working for the UK's Trinity House have staged their first strike in more than 500 years.
The crews help maintain 11,000 aids to navigation in UK waters.
They are demonstrating over pay at the Trinity House office in Harwich, Essex, on Wednesday.
The Unite union has 34 members working on three lighthouse tenders.
They have already taken a day’s strike action earlier this month in their dispute over seven years of below-inflation pay rises, or no increases at all, the union said.
Unite regional officer Miles Hubbard said the protest demonstrated the resolve of members to "seek pay justice and not put up with miserly rates of pay that they have endured over the last seven years.
“In 2017, the employer imposed a 1% increase which Unite members voted overwhelmingly to reject. Talks, including a pay increase for the year starting April 2018, continued, but eventually ran aground.
More action planned
“Unless there is substantial movement by Trinity House management, more industrial action is on the cards during the spring and early summer.”
The Corporation of Trinity House was incorporated by Royal Charter in 1514 to regulate pilotage on the River Thames and provide for aged mariners.
It also licenses deep-sea pilots.
Trinity House told TradeWinds: All our staff are highly valued, but Trinity House salaries are subject to public sector pay policy, and all staff have been awarded the maximum possible within the civil service rules.
"Regular meetings have taken place with the union and Trinity House remains open to consider any proposals which might be achievable within the rules that we are obliged to follow.
"The 2018-19 year has now closed with all staff both ashore and afloat receiving the maximum 1.5% award and we await government guidance for the current year. In terms of the shipping sector in particular, Trinity House believes that the package overall needs to be taken into consideration, which includes a strong emphasis on training and a civil service pension."
