Hicks Gate land could be used to build 1,000 homes
Greenbelt land between Bristol and Bath could be used for some 1,000 new homes.
Liberal Democrat-controlled Bath and North East Somerset Council (Banes) wants to build on brownfield sites.
However, the Planning Inspectorate questioned the feasibility of the plans and told the council it needed a back-up plan.
Four sites are being considered, with land close to Hicks Gate being the preferred option. The plans are being opposed by Conservatives in the city.
Conservative councillor Malcolm Hanny said he was concerned the infrastructure in the area would not be able to cope.
In a statement, Banes said it was looking at options for new housing sites.
It said: "This comes after concerns were raised by a planning inspector who felt there was too great a reliance on brownfield sites."
Councillors will meet to discuss the proposals next Thursday.