Royal Fleet Auxiliary (RFA) seafarers will take strike action on Tuesday in a long-running dispute over pay.
The walkout, the fifth by members of the Rail, Maritime and Transport union (RMT) since the row flared, coincides with Merchant Navy Day.
The union said it has had cordial meetings with the Ministry of Defence but has not received any improved offer.
RMT general secretary Mick Lynch said: “This strike action has extra significance for our members because they will be honouring their fallen comrades in the Merchant Navy while on picket lines in Britain, Australia and around the world.
“RFA seafarers perform a vital role of supporting a range of operations including our Navy and they should be paid properly for such important work.
“We will continue to campaign for a decent pay rise so we can reach a negotiated settlement.”
Officers at the Royal Fleet Auxiliary will also strike tomorrow over pay, their union Nautilus International announced.
The officers went on strike last month for the first time in the history of the RFA.
Nautilus director of organising Martyn Gray said: “Merchant Navy Day is a day to recognise the importance of our nation’s merchant seafarers, securing vital supply chains, particularly in moments of national crisis such as war or the recent Covid-19 pandemic.
“It is therefore deeply disappointing that our members have no other choice but to take a further day of strike action as they reiterate their message that they are overworked, underpaid and undervalued.”
