Rail passengers are being ripped off for millions of pounds by train firms, with customers at Manchester and Birmingham paying 55 pounds for four hours, according to a union on Monday.
The Transport Salaried Staffs' Association, which carried out a survey at 1,000 stations in England and Scotland, said rail companies charged more than 1 billion pounds a year for passengers using the car parks.
It said it cost 135 pounds to park for eight hours at Birmingham and Manchester, while an annual car park ticket at Guildford was 1,790 pounds.
"This is a real scandal and we are today calling on Transport Secretary Geoff Hoon to do something about it," said TSSA General Secretary Gerry Doherty.
"Passengers, like visitors to hospitals, are being ripped off simply because they are a captive audience. They are already paying the most expensive fares in Europe and now we find they are paying the highest car parking charges as well."
Network Rail, which runs many of the car parks, said the union's figures were misleading.
The company, which TSSA said ran the country's 18 largest stations and charged the most, argued that its car parks were designed for short stays.
"They are absolutely misrepresenting the picture of what we charge for short-stay car parks," a Network Rail spokesman said.
He said the first 20 minutes at Birmingham were free and one hour cost 3.70 pounds.
"It's a short-stay car park so longer term it is going to cost you more," he said.
"All that money is invested in the railway and we've got every right to tap into revenue streams. We make no apologies for that."