Workers at the Scottish state-owned ferry operator CalMac were set to begin industrial action on Wednesday of this week.
They are fighting threats to jobs, pensions and working conditions.
The RMT union members plan an overtime and call back ban on Wednesday and Thursday, followed by a 24-hour walkout on Friday.
The workers have received no assurances on jobs or conditions from bosses ahead of a possible takeover by a private operator.
CalMac bosses also want them to pay more and work longer to get lower pensions.
The Scottish National Party (SNP) government is tendering for bids to run ferry services from October next year.
Workers fear a £1 billion contract could be handed to outsourcing giant Serco.