First Great Western is extending its Penalty Fare area to cover stations in Berkshire, Oxfordshire and Hampshire. For the first time the scheme, designed to stop fare dodging, will be extended outside of London.
A FGW spokesman said: "We estimate 5% of people travelling on trains have not bought a ticket which means our honest fare paying customers are losing out."
The new policy means that travellers who cannot produce a valid ticket will be charged at least �20.
Tom Stables, commercial director at FGW, said: "Our experience has shown that often the people who assault staff, commit vandalism and cause problems for other customers are fare evaders.
"So by tackling fare evasion, we are also improving security on the network."
The change comes into force on 31 March.