Argyll Ferries staff were set to join CalMac workers on a 24-hour walkout on Friday of this week over threats to jobs, conditions and pensions.
CalMac, the Scottish state-owned ferry operator, operates the vast majority of Clyde and Hebrides ferry services (CHFS).
It set up Argyll Ferries to run one route about 30 miles outside Glasgow.
Workers at both firms are in the RMT union.
The dispute stems from the Scottish National Party (SNP) government tendering the CHFS contract.
The union is worried that outsourcing giant Serco will take over, as it did NorthLink Ferries in 2012.
This was followed by cuts in services and jobs.
The union wants contracts to include a commitment to no compulsory redundancies.
It wants any changes to staffing levels, conditions or pensions to be agreed with the union.
CalMac workers’ strike two weeks ago had a severe impact on services and created a political row.
Labour has been quick to howl its disapproval.
But the SNP is just repeating what Labour did in 2005 when it ran the Scottish executive with the Lib Dems.
Back then Fergus Ewing, a current SNP minister, said “an SNP government would not tender” CalMac services.