The 24-hour walk out by CalMac staff will mean that only foot passengers will be allowed on the service.

Industrial action over pay, pensions and conditions is set to disrupt 18 out of 26 ferry routes.

Bosses say that they will be able to carry less than half — 40 per cent — of the normal number of passengers across the network during the stoppage.

Passengers are being urged to check the CalMac website for latest service information before travelling.

Martin Dorchester, CalMac’s managing director, said: “Although it looks like this action will be limited in scope, it will undoubtedly still hit the communities we serve hard. It is not just an inconvenience at the start of the tourist season, it will impact island businesses where it hurts most, in their pockets.

“We will continue to work to mitigate as much as possible any disruption for the travelling public and I would like to apologise for any inconvenience and thank passengers for their patience during this time.” Worst affected routes will be those serviced by the company’s larger vessels in Mull, Colonsay, Coll, Tiree and Islay. But a number of the smaller routes that attract large numbers of passengers will operate as normal. Staff on the Cal Mac offshoot Argyll Ferries Gourock to Dunoon route have also been balloted. If they vote in favour of industrial action, crossings could be disrupted next month.

Ferry chiefs warn that passengers using a wheelchair or with large items of luggage or large prams may encounter difficulties during the strike due to narrow access.

Passengers requiring help should contact the CalMac assistance team on assistanceteam@calmac.co.uk or call 0800 066 5000.

For information on sailings visit www.calmac.uk/service-status