UK maritime union RMT’s members in Argyll Ferries and CalMac’s ferry operations will hold a strike on 10 July.
RMT said the decision was confirmed after a vote of nearly 95% in favour of action, following recent industrial action by CalMac staff.
The Scottish Government-run CalMac Ferries operates 27 Clyde and Hebrides ferry service routes. The service term expires next year and, in accordance with European guidelines, the government has requested tenders for the contract.
In response to this announcement, RMT argued that a new contract would be likely to include changes to employees’ current terms and conditions.
RMT general secretary Mick Cash said: "Despite the most strenuous efforts to negotiate a settlement on CalMac, we are still not getting the clear assurances that we seek that will defend the safety-critical jobs and working conditions that go hand-in-hand with delivering safe and efficient lifeline ferry services to the communities that we serve.
"Our members on Argyll Ferries now find themselves staring down the barrel of exactly those same kind of attacks on jobs and working conditions and have delivered a massive and rock-solid mandate for action."
Argyll Ferries previously refused to address RMT’s demands relating to job security, pensions, and the conditions of service.
Responding to RMT’s decision, a Scottish Government spokesman was quoted by BBC News as saying: "We have been continuing to talk with the RMT Union, so it is very disappointing that they feel the need to call further strike action on one of the busiest weekends of the summer for our ferry services."
Image: CalMac Ferries operates 27 Clyde and Hebrides Ferry Service routes which undertake 130,000 sailings every year. Photo: courtesy of RMT.