People living in some of the UK’s most remote and isolated communities are furious after their “lifeline” ferry company told them it was hiking charges for freight by 300%.

News of the rise for residents served by CalMac’s Small Isles ferries – alongside plans to scrap altogether the “loose freight” service on CalMac’s other services – sparked fears that life on Rum, Eigg, Muck and Canna could become unsustainable.

In a surprise email on Monday night islanders were told the changes would be introduced on December 28. Among them was a new weight limit of 100kg, instead of the old one-tonne cap.

The email said: “The previous pricing structure does not reflect reasonable operating costs ... To ensure CalMac can continue to run this service efficiently and in line with health and safety rules, we have had to adapt our pricing and weight structure.”

The changes prompted anger from members of CalMac’s independent Community Board, who represent islanders, when they met CalMac managing director Robbie Drummond on Tuesday.

Community Board chairman Angus Campbell from Lewis said: “If you have a public funded company that’s paid to provide lifeline services ... they have to be working with communities, they should not be making life untenable [for islanders].

“They should not be the organisation that makes life untenable, because part of their remit is to provide a lifeline service.”

Last night, after the board and other community representatives demanded consultation and a rethink, CalMac operations director Robert Morrison agreed to consult with communities, and said the new pricing regime for the Small Isles “is only proposed until engagement with communities and Transport Scotland has taken place.”

But there was no indication the price rises would be reduced, and as a result of the row Kate Forbes, their local MSP and Scottish Finance Secretary, has demanded to speak to senior CalMac staff before the end of the week.

She said: “The first I heard of this proposal was when I was copied into a letter from CalMac. I understand why residents of the Small Isles will be deeply concerned and I will pick this up as a matter of urgency with CalMac.”

The biggest user of the CalMac freight service in the Small Isles is the only shop on Eigg, the most heavily populated of the four islands. Its bulk food containers weighing 270kg would be banned under the new rules. Any smaller items brought in by the new CalMac freight service would face a mark-up of around 70% to avoid making a loss.

Owner Sue Kirk says: “The shop just won’t be sustainable if they don’t climb down.”

She has written to CalMac saying they must reconsider, and added: “I’m not saying they shouldn’t make a small increase, more and more stuff is getting delivered using the service, but the level of increase is just ridiculous.

“They have failed to consult with us.”

Celia Bull, who runs a croft and tourist sailing business on Eigg, said under the new prices her small deliveries this year alone would have cost her an extra £1,400. “If they stick with this it could make island living unsustainable,” she said.

Ewan McEwan, who has lived on Muck for more than 70 years, said: “The Scottish Government says it wants to support islands – they seem to be doing that with one hand and taking it away with the other. A lot of people just don’t have the income to pay these charges.”

The CalMac email also says the loose freight service will be scrapped entirely for other ferries. Islands with larger populations have commercial operators bringing goods ashore in vans and trucks, so Community Board members say the impact on them is likely to be less.

But small businesses on Arran and Bute depend on it for “same day” deliveries of goods such as car spares and flowers, and community leaders there have also protested to CalMac.

Bill Calderwood, chairman of Arran’s community council and also a member of the CalMac Community Board, said the reaction to the move at the board meeting was “very angry”.

“Mr Drummond was resoundingly notified of the community’s views,” he said. “The whole process was just wrong.”

In his statement Mr Morrison said: “A consultation into proposals to alter the service is now under way ... We fully understand the concerns that the potential changes to this service may cause and will work with communities to ensure that these are addressed properly. The Small Isles pricing system is only proposed until engagement with communities and Transport Scotland has taken place.”

“A number of commercial operators already exist throughout the network and we are working to make sure suitable alternatives are in place. We are also working with local NHS providers to ensure critical services are maintained.”