Plans for a new £7.4m "superschool" for children aged three to 18 are likely to face opposition, Vale of Glamorgan council leaders have been warned.
The current site of Cowbridge Comprehensive School would be expanded to include new premises to replace Y Bont Faen Primary School.
Councillors for Cowbridge said new buildings were welcome, but claimed local people did not want the primary school "subsumed" by a superschool.
Consultation begins later this month.
There would also be room for 96 part-time nursery children.
Cowbridge councillors Hunter Jarvie, Andrew Parker and Geoff Cox said they supported the idea of new primary school premises, but did not want the schools to merge.
"We believe that the council should instead look to extending the current good level of co-operation between the two schools," they said in a joint statement.
"Y Bont Faen is a successful primary school which has a good reputation with parents of pupils and the wider community."
Councillor Jarvie added: "There's a lot of local feeling in Cowbridge. They feel the school has got a good history. They don't want it to be subsumed by a superschool."
The council said Y Bont Faen was in a poor condition and has a maintenance backlog worth £301,990 of work.
Councillor Ben Gray was one of two cabinet members who abstained from voting for the consultation, saying: "I'm concerned we're tilting this towards amalgamation from the outset."
Council leader Neil Moore said a preferred way forward was needed for the consultation, but stressed: "If people are against it, we can change it."