LNER will ban passengers from travelling during the coronavirus pandemic unless they have a ticket reservation.
The operator, which runs trains from the North East to Scotland and London, will introduce new safety measures next week, when it is due to ramp up services between Edinburgh, Newcastle and London.
On-board fare passengers will be banned, to help maintain social distancing in carriages, while there will be strict seating rules in place.
A spokesman said: "The safety of our staff and customers is always our top priority.
"To support social distancing for customers who do need to travel with us at this time, all LNER services will be reservation-only from Monday."
Passengers will be asked to ignore their reserved seat and sit in a window seat, with one person per row of four seats, and two rows between each passenger, PA news agency reports.
People travelling as a household will be allowed to sit together but must maintain "a safe distance" from other passengers.
Transport operators are being urged by the Government to rearrange, remove or limit seating "to try and ensure social distancing is observed".
This may include blocking off seats in close proximity to others and removing face-to-face seating.
Passengers are asked to keep a two-metre distance from other people where possible and to wear a face covering.
Services across the rail network will be increased from around 50% of the normal timetable to 70% on Monday, as part of the easing of coronavirus lockdown restrictions.
British Transport Police has been given an additional £1.5 million of Government funding to boost the number of officers at stations in London.
Transport Secretary Grant Shapps said: "Extra boots on the ground working closely with station staff will help manage crowding, provide clear guidance and ensure passengers have the space to maintain social distancing."
Industry body the Rail Delivery Group is urging passengers to avoid non-essential travel after recording a rise in journey planning of nearly a quarter this week.
Passengers are being asked to drive, cycle or walk to their destinations instead of using public transport.
The RDG warned that the capacity of trains will be restricted to as little as 10% of the normal number of people who travel.
