Thousands of rail passengers have been urged to back a union campaign to save hundreds of smaller ticket offices from closure.
The Transport Salaried Staffs Association (TSSA) is to hand out more than 50,000 postcards urging rail users to protest against fears of mass closures.
The union said 675 ticket offices were under threat across the country because of plans contained in the McNulty report into the future of the industry.
The Government and train operators insist no decisions have been made.
TSSA leaders lobbied commuters in London as part of its Better Rail campaign against ticket office closures and rising rail fares, and will target passengers in Cardiff and York tomorrow.
As well as asking passengers to protest to Transport Secretary Justine Greening, the TSSA ask rail users to list what they believe makes a good station for the travelling public.
"Rail passengers need to make their views heard because ministers are determined to implement McNulty through the back door," said union general secretary Manuel Cortes.
"Last week's leaked emails, showing how they planned to blame the train operating companies for the closures, show that the fares and ticketing review now under way is just a political fig leaf to cover the closure plan.
"An unstaffed station is a more unsafe station. It is also more expensive because ticket machines only have a limited range of tickets."