RMT members working for CalMac are preparing to hold a second 24-hour strike on Friday. Union members within Argyll Ferries are also to walk out.
Three days of industrial action by CalMac staff last month culminated in a 24-hour strike.
The dispute has been triggered by the tendering of Clyde and Hebrides ferry services.
Unions have concerns that the new contract will not protect jobs and pensions.
Following a meeting on Tuesday, CalMac said dialogue with the RMT remained "open" with the talks due to reconvene on Wednesday.
The RMT said that, as things stood, the 24-hour strike planned for Friday would go ahead.
Further talks are due to take place between Caledonian MacBrayne and RMT on ferry workers' jobs and pensions.