CalMac has so far successfully moved more than 650 bookings which were scheduled to sail on Friday (July 10) which is threatened by RMT strike action.
The company is continuing to contact the remaining passengers booked to travel on the day to try and rearrange their travel plans.
CalMac is hoping to continue to run nine of 27 routes on the strike day on a normal or revised timetable. Last year on the same day CalMac carried 28,000 passengers around 1500 of them prebooked.
The Arygll Ferries route that links Gourock and Dunoon will operate an alternative bus shuttle service with Western Ferries.
“Our team is working extremely hard to try and lessen the impact this strike will have but we can only do as much as we can, the reality is another strike will again damage the communities we serve,” said CalMac's director of operations, Drew Collier.
“As well as rebooking passengers due to travel we are currently finalising amended timetables and would ask people to continually check our website to see what sailings are going to be running.
“If people could avoid travelling on Friday, I would urge them to think about it, there will be significant disruption.”
The routes the company are likely to keep open are those using smaller vessels – destinations served by its larger ferries: the Outer Hebrides, Islay, Mull, Tiree, Coll, Arran and Colonsay are likely to face a complete shutdown.
“There are also a few occasions such as weddings and commemorative ceremonies that we have pulled out all the stops to accommodate passengers travelling to in the face of this disruptive RMT action,” added Mr Collier.
The company is planning to lay on additional sailings on Saturday to cope with any backlog from the strike. As well as the CalMac website, service updates can also be found via twitter @calmac_updates.