Carwyn Jones says 22 councils is 'not sustainable'
A key report will ask for Welsh councils to be re-organised through mergers.
On Monday, the Williams Commission is expected to suggest existing local council boundaries as the "building blocks", not new lines on the map.
New councils should also be within current health board and police force areas, the report is understood to say.
The commission is expected to call for a cut in the number of councils in a wide-ranging review of public services.
First Minister Carwyn Jones said the current 22 councils is "not sustainable".