Cal Mac may try to minimise the effects of cancelled and disrupted ferries this week by despatching ferries ahead of industrial action, it is understood.
Alternatively, it may reposition vessels and and sail vessels as soon as possible on Saturday, after the strike ends.
Cal Mac's's managing director, Martin Dorchester, said:
“We are disappointed that our dialogue with the RMT to avert industrial action this week has broken down.
“Our offer to provide assurance that we would include a commitment on no compulsory redundancies in our bid submission in return for the RMT calling off the industrial action planned for later this week was rejected.
"We were also willing to work together with both the RMT and TSSA [one of four unions Cal Mac is negotiating with] over the coming days to agree a form of words in our collective agreements which would provide greater protection to employees around terms and conditions of employment.
Cal Mac: strike disruption is inevitable
22 June 2015
“Unfortunately this was also rejected.
“Failure to keep these discussions alive will be a disappointment, not just to those who will be losing pay this week, but to potentially thousands of travellers of who will be disrupted.
"The threat of strike action also has major potential to damage the economies of the communities we are part of.
“We are currently working on alternative timetables and contingency plans and will be doing all we can to ensure that disruption to these lifeline service are kept to a minimum.
“However, the travelling public needs to be aware that disruption is inevitable and that they should consider careful whether their trip is essential before travelling later this week.
“Our door remains open. We urge union representatives to re-
"Our aim is to do everything possible to avert any industrial action which will impact our ability to maintain the lifeline services we provide.”