The proposed structures of Durham and Northumberland's new unitary authorities are being scrutinised to ensure "electoral equality".
The Boundary Committee for England has begun a public consultation exercise looking for local views on electoral boundaries in the two counties.
It wants to ensure all councillors in the new authorities represent about the same number of voters.
The first stage of the consultation ends on 15 September.
Chair of the committee Max Caller said: "In this phase of the review, we will be looking for information about a number of factors to help us consider the most appropriate number of councillors for the new authority."
Two further stages of public consultation are planned and the review is expected to be completed next summer.