Willie Rennie, MP for Dunfermline and West Fife, has tabled an Early Day Motion in the House of Commons calling for all party support for the "Fife fares, not fair" campaign.
The campaign was first launched by Harry Wills, Liberal Democrat candidate for the Glenrothes by-election, and is supported by Tavish Scott and Nick Clegg, as well as by fellow Fife MP Sir Menzies Campbell.
The motion highlights the disproportionate cost of train fares from Fife compared to other parts of Scotland.
Commenting Mr Rennie said:
"It's inexplicable that a train journey to and from Fife can cost £90 a month more than an equivalent journey outside of the Kingdom."
"It doesn't make any sense that commuters should be forced to pay a penalty price simply because they live in Fife."
"One of the great pluses of the train is its benefit to the environment; but with fares this high many people will stop being conscientious and start using the car to save money."
"When I speak to commuters they are visibly outraged by train fares across the Kingdom. With the support of my Liberal Democrat colleagues, I will continue to fight until Fife train fares are fair."
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