A teaching union has questioned the "educational rationale" behind plans to create a "super college" in Glasgow.
The Educational Institute of Scotland (EIS) said a three-college merger plan would "lead to fewer student places than are currently provided".
Central, Metropolitan, and Glasgow Nautical Colleges are involved in the £300m "New Campus Glasgow" project to create the City of Glasgow College.
Its principal said the project would provide more, not fewer student places.
The new single campus would cater for up to 50,000 students.
The concerns of the EIS have been outlined in a letter to Scottish Education Secretary Mike Russell by union general secretary, Ronnie Smith.
The letter questions the "educational rationale" behind a move that will "result in fewer student places".
It expresses concern that "a guarantee of no compulsory redundancies" has not been made and states that "insufficient progress" has been made towards "harmonisation of pay and conditions" for staff at the colleges.
Mr Smith also calls for Stow College - which is in Glasgow - to be "brought fully into the merger process" as its future "hangs in the balance".
He concludes: "It is clear that this proposed merger has not been thought through sufficiently, and that a great deal of clarification is needed before these proposals can proceed.
"The Cabinet Secretary for Education and Lifelong Learning, Mike Russell, should withhold approval of the proposed merger until all the outstanding issues are addressed.
"We all want to see a brighter future for further education in Glasgow, but it would be unwise to push ahead with the current merger proposals before all the issues are addressed and all the alternatives are considered fully."
Principal Designate for the City of Glasgow College, Paul Little, said he would be contacting Mr Smith to stress the clear benefits of the merger plans and that his concerns over compulsory redundancies were unfounded.
He said: "I am very convinced that there is a strong rationale, a strong educational rationale, for this merger and there are clear academic benefits."
Mr Little said "involved, detailed and complex" discussions were taking place on the issues of conditions of service and that he had already indicated to staff that there was no threat of any compulsory redundacies.
Mr Little said: "I am at a loss to understand why, if that was said publicly and also when there was a clear and explicit reassurance statement in the merger proposals, that is still an issue.
"I recognise that that's an anxiety amongst members of staff and academic support and I think that's why I'm disappointed to read that - because I was quite explicit in front of all the assembed staff, which is quite a bold statement to make in front of so many staff, to say that we have no plans, either private or publicly, to make any compulsory redundancies."
He said this was a very complex three-way merger but that it would improve choices for students, safeguard specialist learning, enhance employability and improve university access.
Mr Little also reiterated his call for Stow College to be included in the merger.