Plans to redevelop Birmingham's New Street Station could be delayed by up to a decade, unless more people pledge their support to the project.
A campaign is being launched to highlight the importance of the £100m Gateway for Birmingham scheme.
It needs to be included on a priority list, due to be completed before Christmas, to secure funding.
Rail passengers are being asked to send in postcards and letters to be given to the government later this month.
BBC Midlands Today's transport correspondent Peter Plisner said overcrowding at the station has become a serious concern.
New Street handles more passengers than Gatwick airport does and has more trains passing through it each day than the number of planes that pass through Heathrow.