CalMac is stop taking bookings on all ferries before July 15 in response to the ongoing Covid-19 pandemic.
Priority on all journeys will be given to emergency services and medical emergencies during the four-month window.
The operator said it would honour existing bookings for services during that timeframe, identified by the Scottish Government as being likely for disruption.
Bosses said the decision had been made to help plan for the impact of the virus on staff numbers.
The firm operates ferries in the Western Isles.
CalMac will also stop serving hot food on board from today in an effort to free up staff for crew.
Managing director Robbie Drummond said: “The Covid-19 outbreak is creating an ever-changing landscape not just for CalMac but for all transport operators and indeed all businesses.
‘Whilst we are currently able to continue operating our normal timetabled service we have to plan for the impact of the virus on our staff on vessels, ports and support services.
“It has been prudent, therefore, to put in place an immediate stop on customers being able to book services in advance.
“We will effectively be operating a turn up and go service on all of our routes.
“This will reflect arrangements we already have in place permanently in a number of locations across the network.”
