Members of Cleveland Police Authority have told Home Secretary Charles Clarke they will try to block plans to create a North East "super force".
Mr Clarke is backing proposals to merge Cleveland Police with neighbouring Durham and Northumbria forces.
It is part of a restructuring project which could see the number of police forces plummet from 43 to just 12.
But Cleveland Police Authority members have warned they will refuse to co-operate with merger plans.
The Durham and Northumbria forces have backed the merger proposals as "the only way forward" for policing in the region.
But Cleveland Police Authority is angry that an option to create a Tees Valley force - to cover the current force area and south Durham - was not considered.
Now, in a strongly worded letter to Mr Clarke, senior members of the authority have warned of a bitter campaign to block the creation of a so-called super force.
Signed by Middlesbrough councillors Barry Coppinger, Ron Lowes and Hazel Pearson, the letter states: "Under all circumstances Cleveland Authority colleagues will not co-operate with any voluntary merger proposals around a regional force."
They say they will be "fighting against them, using all means necessary, in full knowledge of legalities, and going all the way to the floor of the House of Commons if that is required."
The authority says it has concerns over how much a regional police would cost and how effective it would be at tackling local issues.