Rail commuters have expressed outrage following increased car parking charges at stations just days after train fares rose by an average of 4.2 per cent.
The Transport Salaried Staffs' Association said that passengers were being treated as "cash cows" by train operators.
An annual car parking ticket at High Wycombe, Buckinghamshire, has increased from £960 to £1,040, an eight per cent rise, while a weekly ticket to park at Hitchin, Hertfordshire, has gone up from £31 to £32, said the union.
General secretary Manuel Cortes said: "These firms are squeezing passengers until the pips squeak. While fares are controlled by ministers, there is a free-for-all on car parking charges. Rail firms simply charge what they think they can get away with.
"It is a scandal that they are increasing charges by as much as five times the rate of inflation. This is daylight robbery at a time of falling living standards."
The union has called for car parking charges to be regulated in line with fares as part of the rail ticket price review currently being conducted by ministers.
Meanwhile, weekday parking fees at London Underground stations have increased by an average of 18.73 per cent - going up from £4.27 to £5.07.
Transport for London said the increase was the first for more than two years and would bring prices more in line with other local car parks.
A spokesman for the Association of Train Operating Companies said: "Many stations don't charge for car parking and where operators do put up prices, much of the money raised goes towards the running cost of the railways in line with the Government's policy to increase the contribution from passengers and reduce the share from taxpayers."