Customers who had already made bookings with Brittany Ferries from the south coast of England were sent messages saying that their original sailings had been cancelled, but that they would be booked onto alternative routes.
It was announced in December that the holiday ferries firm had signed a £46.6 million deal with the government to increase its freight sailings. It said it had changed its timetables to increase sailings by 19 a week on three of its key crossings to allow it to bring "vital" goods such as medicines across the Channel.
One customer, Sue Staunton, who is now based in England, but until recently lived in Crieff, was told by email that her return trip from France in May had been rescheduled.
The firm said: "I'm writing to confirm that your sailing on 12/05/19 on board the Barfleur is among those affected by the government's initiative to create additional freight capacity for the transportation of critical goods (such as medicines) across the Channel. I'm sorry to advise that your sailing from Cherbourg to Poole has been cancelled but can confirm we have rebooked you onto the revised schedule."
She told The Scotsman: "They rebooked me on the morning one that day which is totally inconvenient for us. It’s a holiday, but we have a long drive up through France to get to Cherbourg.
"That was for May and I have a similar booking in June which I'm waiting to see if they also cancel. Clearly medical supplies take priority, but this is a ludicrous and entirely unnecessary situation we all find ourselves in. More pertinently, it’s backlash to inconveniences like this which will potentially spark a much bigger reaction."
A spokesman for Brittany Ferries said the affected crossings were between Poole and Cherbourg, Portsmouth and Le Havre and Plymouth and Roscoff.
He said: "We are increasing the number of sailings every day from 30 March rather than cancelling routes, but as a result have had to change our timetables. We this weekend published our new timetable and have begun contacting customers who have already booked sailings after 30 March."
He added: "We will do whatever we can to minimise the inconvenience for customers as a result of the changes."
He added that around 10 per cent of customers who had been rebooked had already contacted the firm to alter their booking.