A planning meeting to decide the future of Horkesley Park, near Nayland, has been delayed by a fortnight.
The application, to build a conservation and heritage centre on the site, is the fifth to be submitted over the last decade by Bunting and Sons and is being supported by planning officers.
However, objectors, led by the Stour Valley Action Group, believe the recommendation is “seriously flawed”.
Chairman Will Pavry said: “Our task is to convince councillors on the planning committee they must reject the application against the advice they are likely to receive from officers but in line with the findings of their own planning policy department and external consultants.”
The group is calling a meeting at Little Horkesley Village Hall on Wednesday at 7pm to discuss tactics and further action.
Around 700 letters and emails objecting to the Stour Valley Visitor Centre have been received from individuals and organisations.
These include the Dedham Vale AONB and Stour Valley Project, the Dedham Vale Society, Nayland with Wissington Conservation Society and adjoining parish councils.
Colchester Borough Council will rule on the plans on February 28.