Campaigners accuse Deputy First Minister and Infrastructure Secretary Nicola Sturgeon of letting down "the population of Cowal, wider Argyll as well as Inverclyde" by closing the door on a replacement vessel this winter.
The Dunoon Gourock Ferry Action Group wants the return of a car ferry to the service between Gourock and Dunoon piers, formerly operated by Caledonian MacBrayne .
It was lost when the privately owned Western Ferries was given a monopoly on the route in 2011 because ministers tendered it as a passenger-only service, now operated by CalMac's sister company Argyll Ferries.
But the campaigners identified a CalMac car ferry which could do the job – the MV Coruisk.
Alex Neil, the former cabinet secretary for infrastructure, said he would look at whether it would be possible to replace the AliCat, which campaigners branded a "bathtub boat".
Ms Sturgeon says she has asked Transport Scotland for options for the short term but it will not be possible to deploy a substitute vessel this winter. She has been told the Coruisk could not deliver improvements on the timetable, given its high level of cancellations due to weather.
But Kenneth Barr, spokesman for the ferry action group, said "This is a complete load of utter balderdash, demonstrating the utter incompetence, ignorance and duplicity of Transport Scotland."