A Northampton history group says the upcoming dissolution of the borough and county councils threatens to halt years of progress for projects across the town.
Friends of Northampton Castle have been campaigning since 2011 to create a heritage park near the Chalk Lane car park in an ambitious landscaping project.
They secured planning permission in 2018 - but now the group fear their work will be halted and delayed in the face of a complete overhaul in Northamptonshire's local government structure voted in August last year.
The county and borough council voted in August to dissolve themselves and form two unitary governments across Northamptonshire.
Now, the Friends say they are only one of many projects in the county that could be disrupted by the changes to local government.
Chairman of the Friends Dr Marie Dickie OBE said: "We are concerned that the very process of de-constructing local councils will result in a lack of focus such projects as ours.
"While the councils spend their time and energy on trying to manage these changes, there is likely to be even less interest shown in supporting the sense of identity and community pride which heritage projects such as ours can bring.
"In these circumstances, we cannot support the proposed reorganisation."
Early forecasts suggest that the county council is faced with making some £60million of savings in time for their budget in 2019-20.
Dr Dickie is concerned the reformation of the councils and challenges it could present to budgets could leaving community projects by the wayside.
The Friends voiced their concerns in a letter of response to an ongoing consultation over the unitary proposal.
The Friends' plan includes a new 'play maze' and heritage footpath based on the grounds and footprint of the historic medieval Northampton Castle.