Hundreds of Royal Fleet Auxiliary workers are to begin industrial action from midnight in a dispute over pay.
Around 700 workers will take part, with the exception of those taking part in humanitarian or disaster relief operations.
Staff voted for action in protest at the imposition of a 1.5% pay rise, which they say is behind the cost of living.
They have the support of the Rail, Maritime and Transport union (RMT), which says the salary increase amounts to "a pay cut" when looked at in real terms.
The campaign of action will include only working contracted hours, and not preparing food for social functions such as cocktail parties.
The RFA is a merchant navy organisation with a fleet of 12 ships, providing medical care, kit and fuel to the Royal Navy and Royal Marines.
As well as other taskings, the four RFA ships will also support Britain’s new aircraft carriers, HMS Queen Elizabeth and HMS Prince of Wales.
In a statement, RMT General Secretary Mick Cash said: "It is frankly disgusting that this government, who are very fond of praising our forces when it suits them, are trying to impose a pay cut on the brave men and women who supply the Royal Navy in danger zones and humanitarian missions around the globe.
"RMT will not stand by while RFA staff are denied basic pay justice," he added.
In response, the Ministry of Defence has said: "We are aware of the RMT’s decision to undertake industrial action and are assessing their proposals so we can take appropriate measures to ensure operations continue during this period.
"The pay rise for Royal Fleet Auxiliary personnel for 2018/19 was set in accordance with Treasury guidance."
The RFA action is scheduled to continue until further notice.