Welsh Conservatives have pledged to give free bus travel to all 16-24 year olds in Wales, and have urged Labour ministers to do the same.
The Green Card - which the Tories said could cost up to £25m a year - would also give a third off rail tickets.
Education spokesman Darren Millar said young people suffered high car insurance and the lowest wages.
The Welsh Government dismissed the plan as "fantasy economics", saying it would consult on a new discount travel pass.
The current MyTravelPass scheme gives 16-18 year olds a third off bus fares.
Mr Millar said the Welsh Conservatives' "exciting offer for young people" would also protect the environment and help save local bus routes from the axe.
His colleague Russell George, the Tories' economy spokesman, added that travel costs could be a "huge barrier" to education, training and job opportunities.
'Fag packet' economics
"We are committed to building a stronger economy and a fairer society, and we believe that young people should benefit from the same travel concessions offered to Wales' over-60s," he said.
The Conservatives said the scheme would be funded by scrapping the education maintenance allowance (EMA), which they have previously proposed.
A Welsh Government spokesman said: "These Tory proposals have been made up on the back of a fag packet.
"To think you can provide 350,000 people with free bus travel and a third off rail fares for £25m is fantasy economics."
The spokesman added that the Welsh Government would be launching a consultation next week on plans to launch a replacement for MyTravelPass in April.
"It will be a discounted travel scheme grounded in reality, that can encourage more young people onto Welsh buses," he said.