Teachers and unions have called for plans to remove sixth forms from English-medium schools to be blocked.
Torfaen council said moving post-16 provision to a new £20m facility in Cwmbran from September 2019 would benefit pupils.
But unions fear experienced staff could be lost through redundancies.
They said some pupils could also face longer journey times and fewer course choices.
The council said the "anticipated funding environment" would mean a wider range of academic courses would be available than would otherwise be the case.
But there have been calls for the Welsh Government to intervene.
In 2015, a plan for a larger college with an engineering school of excellence was rejected.
This second proposal is for a smaller college without the engineering school to replace sixth forms at St Albans, Croesyceiliog and Cwmbran secondary schools.
It would be run on the council's behalf by Coleg Gwent, which already provides academic and vocational courses across south east Wales.
School inspection body Estyn said it was likely the plans would at the least maintain the current standards achieved by the pupils.
But it added the council had not considered the effect on pupils from low-income families and did not sufficiently outline how disruption would be minimised.
Sophie Toovey, an English teacher in Pontypool, said moving the sixth form "creates more barriers for students."
Sophie Toovey, an English teacher at St Albans in Pontypool, said: "We have a lot of students from further up the valley and if we close down our sixth form and we have a college built further down in Cwmbran that creates more barriers for disadvantaged students to access further education.
"We also feel strongly that pupils want to stay in sixth form because it's a nurturing environment where they're familiar with their teachers - that relationship's been built up since Year 7."
NUT Cymru secretary David Evans said as redundancies were part of the plans, there was a danger of losing experienced teachers.
"There is nothing in the proposal that suggests Coleg Gwent will be able to match the high quality of provision, pastoral care or continuity of education that has delivered these rewards in the past and that is a major concern for the youngsters, their parents and the wider community," he said.
Jane Setchfield of NASUWT added: "High quality teaching staff could be lost to the community with no measurable gains."
A council spokesman said the proposals offered a "far wider range and quality of academic courses" and would remove unnecessary duplication and spend.
The council agreed some pupils would have to travel further, but said for others it would be closer than current arrangements and it was supported by direct bus services, with investigations under way looking at highway improvements.