The west coast operator struggles to meet demand on its busiest routes, but some passengers make multiple bookings for different sailings to keep their travel options open, as they can get full refunds for cancelling them.
However, CalMac said some of these bookings were cancelled or rolled forward at the last minute, leaving other drivers unable to travel even though there was spare space abroad.
The company plans a sliding scale of charges for cancellations, with the “cancellation levy” ranging from 25 per cent of the vehicle fare if a booking is cancelled 29 or more days in advance, to 100 per cent of the fare for less than 24 hours notice.
Cancellations made between eight and 28 days before travel would incur a 50 per cent deduction, while those made between 24 hours and seven days would incur a 75 per cent deduction.
In addition, passengers would only be permitted to change their bookings up to 48 hours before travel, which would incur a £10 “amendment levy”.
Exemptions would include the death of an immediate family member, debilitating illness preventing travel, involvement in a road crash, a multi-vessel journey where one leg of the journey was cancelled by CalMac and the NHS cancelling an appointment.
The penalties would not include block bookings for commercial vehicles.
In a letter to MSPs, CalMac commercial director Diane Burke said: “These changes would address a significant problem – at the moment there is no incentive for customers to give us early notice of changes or cancellations to their booking.
"Some customers therefore cancel their bookings at very short notice.
"This results in unused deck space, thus denying other customers the opportunity to travel.
“This proposal is aimed at discouraging those who make multiple reservations, then cancel the ones they no longer require at late notice, often too late for us to reallocate the space."
Ms Burke said ferry traffic had increased by 37 per cent over the last seven years following the introduction of fare cuts under the “road equivalent tariff”, designed to bring the cost of sea and road travel into line.
She said the eight ferry committees and transport forums representing passengers would be consulted on the proposals, and findings from the process published in June.
In a letter to MSPs, CalMac communications director Stewart Maxwell said: “We hope these proposals will be welcomed by those who have complained about vessels sailing with spaces available, despite it being ‘fully booked’ in the days ahead of departure.”
Joe Reade, chair of the Mull and Iona Ferry Committee, said: “We acknowledge that ‘no-shows’ are a problem for the service.
"We are not convinced, however, that punitive charges are the best or fairest way to address this problem.
"There are often many legitimate reasons for failing to arrive at a sailing on time – for example, as a result of traffic delays.”
Scottish Labour transport spokesperson Colin Smyth said: “The utter failure of the Scottish Government to deliver the ferries our island communities need is the reason so many people appear to be making bookings speculatively so far in advance.”