Wales now looks certain to have a single national police force.
Opponents say making four forces into one would damage policing
Home Secretary Charles Clarke says one force instead of four is the only "suitable" option, which supporters argue is needed against terrorism, drug trafficking and organised crime.
But there was strong opposition, with North Wales Police Authority chairman Ian Roberts accusing Mr Clarke of "acting like a bully".
Plaid Cymru, Conservatives and Liberal Democrats also voiced their anger.
The number of forces in Wales and England could be cut from 43 to as few as 12 under outline plans published by Mr Clarke on Thursday. Forces have to submit their preferred options by 23 December.
In two areas - Wales and north-east England - Mr Clarke indicated that only a single force would get his backing, and that "other stand-alone and merger options were assessed as unsuitable".
Two weeks ago the Dyfed-Powys, Gwent, South Wales and North Wales Police authorities submitted three options to the Home Office.
Home Secretary Charles Clarke would back only an all-Wales force
They were: to keep the existing four forces (with North Wales Police having greater partnership with Cheshire); merging existing forces into two; or merging all four into one.
'Exceptional crime-fighting record'
Mr Roberts said: "Mr Clarke's idea of consultation is a nonsense. He is acting like a bully who expects everybody to bend to his will at the drop of a hat - no matter how unreasonable he is being."
Mr Roberts pointed to North Wales Police's "exceptional" crime-fighting record and claimed one force would not improve policing in the area.
"It is no accident that recent years have seen growing co-operation between north Wales and the north west (of England) - a relationship that has developed purely because of reality of how things are."
Plaid Cymru's Leanne Wood said: "This announcement shows utter contempt for devolution, local government and the police.
"New Labour has effectively reorganised Welsh police forces in a single press statement. They have not even had the courtesy to wait to hear the final view of the assembly or the police constables in Wales.
Supporters say an all-Wales force would be best to combat terrorism
Nick Bourne, leader of the assembly Conservatives, said: "Creating an all-Wales force would take policing away from the people and could undermine the police's ability to detect, fight and solve crime.
"It is vital that we continue the fight against crime, but I believe an all-Wales force will increase bureaucracy and have a serious impact on efficiency."
Mike German, leader of the Lib Dems in the assembly, said he was "outraged," and claimed Labour was "rushing out" its announcement to deflect attention from its Commons defeat over terrorism the night before.
"The original consultation period was too short to start with," said Mr German. "Now Charles Clarke has short-circuited what little time there was and made up his mind for Wales."
A Brecon-based project team, led by South Wales deputy chief constable Paul Wood, has been assessing all the options on behalf of the four forces.
Mr Wood said that while the Home Office was backing only the single force, it also said the police authorities could continue to evaluate the options, and they would still do so.
When chief constables gave evidence to the Welsh assembly earlier this month, they said that on paper an all-Wales force would best meet government targets on how to tackle cross-border crime and terrorism.
But they would not say whether that was the option they supported.