Workers who refuel naval ships will stage a series of strikes in a row over rotas.
Unite members employed by Serco at the Devonport dockyard in Plymouth will take industrial action every weekend from Friday until the end of April.
Under the current rota system, Unite said workers are not told if they will be working over the weekend until Friday afternoon.
“Such Victorian-style working practices are shameful in the 21st century.
“Our members employed by Serco at Devonport have the union’s unfailing support in their fight for fairness and decency.”
Salli Shapcott, Serco capability director for air and maritime, said: “Serco is disappointed at this industrial action by a small group of our employees at HMNB Devonport.
“We have been consulting with Unite at both a local and national level since November 2021 over working patterns. Serco remains open to further discussions to resolve the dispute.”