Rail passengers have been urged not turn up without an advance ticket and to wear face coverings when they travel on the West Coast Mainline.
Avanti West Coast made the announcement as part of new social distancing on its services between Glasgow, Manchester, Birmingham and Leeds.
Passengers might be refused travel if the guidelines are not followed.
The measures take effect on Monday and Avanti says it may not allow carriages to be more than a quarter full.
“We’re appealing to our valued customers to help us and other passengers by only travelling with a reservation,” said Avanti West Coast’s managing director Phil Whittingham.
“If everyone does this, we’ll be able to keep social distancing in place on board, both for our customers and our people.
“If customers do turn up without a reservation, we’ll do our best to help but we can’t guarantee they’ll be able to take the train they want.”
Because of this, the train operator is asking passengers to book in advance on the Avanti mobile app where possible, to avoid using facilities at the station or handling cash.
People should also check before they travel, in case the time of their train has changed.
Other measures being introduced by Avanti include face masks for staff and waiting rooms and lounges will be shut.
There will also be enhanced cleaning procedures onboard trains and at stations, especially focused on cleaning door buttons, grab handles, tables and all touch points, as well as equipment like phones, chip and pin machines, self-service ticket machines and point of sale systems.
Shops onboard Voyager services, which travel between London and destinations like Blackpool, Shrewsbury, Birmingham, Edinburgh and North Wales, will be closed and no food and drink will be available.
The shops on Pendolino services will still be open, but re-usable coffee cups will not be accepted.
Increased train services
A new timetable is being brought in from Monday, in line with updated travel advice from the government that will see train services increase to about 70% of the normal timetable.
During the coronavirus pandemic only half of normal rail services have been running.
The easing of travel restrictions is likely to be done gradually – the government has suggested that working hours might be staggered to limit passenger numbers.
People in England who are allowed to return to work have been asked not to use public transport if possible.
If maintained, the two-metre social distancing measure would cut capacity on trains by up to 90%.
A recent Transport Focus survey suggested more than 60% of UK passengers would not feel comfortable using public transport unless social distancing was in place.
It found 51% would not be happy unless passengers were required to wear masks.