RMT union members working for Caledonian MacBrayne are to hold a second strike on 10 July.
It follows industrial action by CalMac staff last week which culminated in a 24-hour strike on June 26th.
The dispute has been triggered by unions’ concerns about the new contract to run the Clyde and Hebrides ferry services.
CalMac’s current deal to operate the network comes to an end next year.
The Scottish government has put the contract out to tender, in line with European rules.
The unions have raised concerns that, regardless of who wins, the new contract will see changes in employees’ current terms and conditions.
In response to the news CalMac Ferries, managing director, Martin Dorchester said: “We are extremely disappointed that the RMT has chosen to continue with strike action.
“The best way to protect the existing terms and conditions of its members is to work with us to ensure we win the Clyde and Hebrides Ferry Service contract and this action is damaging.
“We are anxious to avoid any more disruption which is not in the best interests of our employees and the communities we serve and would urge all our colleagues to turn out for work.”