East Midlands Trains is introducing a fresh crackdown on passengers evading fares with a new penalty system.
Those travelling without a valid ticket will have to pay £20, or twice the full single fare, to the next station, whichever is the greater amount.
They will then have to pay a full single fare to their final destination.
A spokesman said the new system, starting on 7 December, would be more streamlined as some fixed penalties could be imposed straight away.
The company introduced ticket barriers at many stations earlier this year to fight fare evasion.
The new system is being introduced with the backing of the Department for Transport following consultation with stakeholders.
Penalties will also apply for those carrying discounted tickets without a valid railcard, or travelling first class on a standard class ticket.
Managing director of East Midlands Trains, Tim Shoveller, said: "Our advice to customers is simple - please make sure you leave enough time to buy a ticket before you board the train.
"Millions of pounds are lost every year through fare dodging - this is money that should be going back into improving trains and stations to make sure that passengers get the service they expect and deserve."