Gwent police force - the only single-county force in Wales - opposes amalgamation with South Wales police, which covers West, Mid and South Glamorgan.
Under the local government reorganisation proposals, there are three options for the forces: amalgamation; Gwent to expand by taking over the policing of Rhymney Valley; and South Wales to take over Islwyn from the Gwent force.
Gwent police authority argues its force has better performance than South Wales and that Rhymney Valley DC and local MPs back the plan for Gwent to remain separate and expand.
South Wales police authority backs Islwyn transferring from Gwent. As this would reduce the Gwent force so much it would no longer be viable, amalgamation would be bound to follow.
The matter will now be referred to the home secretary.