A "whole generation of young people" will be unable to get to further education college because of cuts to public transport spending.
That is the claim by the National Union of Students in Wales, who say most learners rely on public transport.
Bus operators have been reviewing services after support grants were cut by 25% last year.
The Welsh government said it was looking for innovative solutions to deliver a sustainable bus service.
Research by the National Union of Students (NUS) in Wales found that six in 10 further education students had costs associated with travel, with one in five paying £20 or more a week.
It also found that 30% of those who responded to the research did not receive any form of financial support for transport, while 69% who receive some form of transport support rely on it to travel to college.
The deputy president of NUS in Wales, Beth Button, told BBC Wales: "These young people who cannot afford to get to education, it means we're going to have a whole generation who aren't going to be able to get to college.
"For many of these students, further education is their second chance. We talk about further education and college education being a second opportunity for vulnerable learners and people having a second chance.
"And if these students can't afford to get to college then we're removing that opportunity from them."
Steffan Thomas, from Llandysul in Ceredigion, travels 30 miles (48km) each way by bus to his college in Llanelli.
He said: "It takes an hour and a half, hour and three-quarters every morning and every night.
"I leave the house at 6:45 in the morning and I won't be back until 5:30-5:45, depending on traffic, and when you do that in a day it takes a lot out of you and you get tired easily. It's harder to concentrate in college because you've been awake for many hours."
A Welsh Local Government Association spokesman said while local councils in Wales were committed to protecting access to education for all learners in Wales, there was a collective shortfall of £290m in the local government budget for the coming year.
"Changes to existing post-16 transport arrangements are also being driven by wider economic factors such as the closure of routes by local transport operators because they are not economically viable within the current economic climate," added the spokesman.
A Welsh government spokesman said: "The transport minister is looking for innovative solutions to deliver an efficient, sustainable bus service across Wales and has established a new bus advisory group to review policies and look at new approaches to funding.
"But local authorities are responsible for determining how they spend the funding we provide and identify which services should be supported and at what level."