Quarantine rules for those returning to the UK from France came into place last week, after Spain was added to the list in July.
As a result, Brittany Ferries has announced cuts to its network, including long-standing routes to both France and Spain.
Here’s what you need to know.
Which routes are being cut?
The long-standing routes from Portsmouth to St-Malo in France and Bilbao in Spain have been dropped by the firm.
On other routes, there will now be fewer sailings, after the French ferry company said demand for autumn sailings is “extremely weak”.
Which ships will stop running?
Brittany Ferries resumed limited operations in June, more than three months after they suspended trips due to coronavirus travel restrictions.
Brittany Ferries currently has eight ships, but two of these - Armorique and Bretagne - will be laid up, and a third ship, Etretat, will not return to service as previously planned.
Armorique, serving the Plymouth to Roscoff route, will be laid up from 31 August.
Bretagne, currently serving the Portsmouth to St Malo route, will be laid up from 7 September.
Which routes will continue?
The remaining ships will still operate, but on a much-reduced service. The operating routes are Portsmouth to Cherbourg and Le Havre, and from Plymouth to Roscoff and Santander.
Brittany Ferries normally operates routes from Portsmouth and Plymouth to Santander and Bilbao and cross-Channel ferries to France from Cork, Plymouth, Poole, Portsmouth and Rosslare - although Poole was not being served this summer.
Why is the company making cuts?
The company said that quarantine measures were having an "immediate and profound" impact on demand for travel.
Christophe Mathieu, director general of Brittany Ferries, said: “We warned over the weekend that schedule changes were likely, as quarantine measures have led to a significant drop in demand for our services.
“This is not something we want to do. However, in the context of a terrible summer season we have no choice but to consolidate sailings that, by virtue of lack of passenger numbers, are uneconomic to run.
“These extraordinary decisions are regrettable and we apologise in advance to all those whose travel plans will be disrupted.”
How many customers will be affected by the changes?
Around 50,000 passengers with existing bookings will be affected by the changes to the schedule.
What should I do if I have a ticket booked?
The company is now working to accommodate displaced passengers on other services.
However, the ferry firm requests passengers wait for notification of any change to their booking.