The state-owned company is planning to phase out its season tickets, which cover 12 or six month passes with three month and weekly tickets also available.
Islanders on Cumbrae have objected to the plan, with the 10-minute journey commonly made by residents for shopping, with some commuting to work and others for education.
Under the proposals, the price of a journey will rise from £2.08 under a 12-month season ticket to the regular fare of £3.50 – a rise of just over 40 per cent.
CalMac said the season tickets were not meant to be sold under Road Equivalent Tariff rules, which were introduced fully in 2015 to bring in a fairer, more affordable pricing structure for ferry crossings. The season tickets have remained for sale to islanders in some cases, but are not advertised, it is understood.
Councillor Alex Gallagher (Labour), Islands Convener and Cabinet Member for Economy at North Ayrshire Council, which covers Largs and Cumbrae, said: “It is a mistake to take away these season tickets and Cal Mac should re-think the situation.
"The Road Equivalent Tariff scheme was meant to reduce the cost of travel to the islands but the trip between Largs and Cumbrae is very short and, when you put it through the RET calculator, there was no reduction in the cost. The season tickets were continued on a discretionary basis.
"The passes weren’t advertised and they are not in the standard brochure, but islanders were able to come on and off the islands at a reasonable cost.
"I have no idea why they have decided to take them away now. I would urge them to greatly rethink this move as I think it is an injustice to islanders.
“Islanders already face higher costs – this could make things even harder for them.”
Other short routes in the area will also have the season tickets withdrawn with the passes no longer available for journeys from Wemyss Bay to Rothesay, Colintraive to Rhubodach and Oban to Craignure.
The Cumbrae and Travel and Tourist group has also criticised the move by CalMac.
A statement said the increases would “massively effect” those who commute to and from the islands.
“This will have a detrimental effect on affordability for those travelling on the ferry for work, education, childcare and many other individual reasons.”
CalMac denied a claim from the group that fares could rise by 50 per cent and said that a limited proportion of travellers would be affected. Q dozen yearly passes are in use on the Largs to Cumbrae route with more than 450,000 passengers carried on the route every year.
A spokeswoman for CalMac said: “Since Transport Scotland introduced Road Equivalent Tariff (RET), which provides discounted ferry travel, we have been phasing out products such as season tickets. The rules regarding RET state that additional discounts on top of what are already cheaper tickets should not be sold.”
A spokesman for Transport Scotland said the RET scheme had led to an estimated average fare reduction of 34% for passengers and 40% for car traffic and “continues to save travellers around £25 million a year”.