All four police authorities in Wales have now rejected plans to merge with the three other forces.
Gwent Police Authority became the latest on Thursday when after a special meeting it said it did not have the information to make a decision.
Home Secretary Charles Clarke has given them all until Friday to accept the plans or he will press ahead.
Chairman Geraint Price-Thomas has said there are still concerns about finance and pace of reform.
In a statement released after the meeting, Gwent Police Authority said members had found "insufficient evidence" to support a merger.
It added: "Members conveyed their disappointment that questions around finance, governance, human resources and public consultation remain unanswered.
"Should any further information come to light over the coming months, this will be brought back to the police authority for consideration."
Members asked the Home Office for more information on the plan for a single Welsh force after the authority last met on 10 February.
Under current legislation, if there is no support for a voluntary merger from the police authorities, Mr Clarke can seek a merger himself.
Mr Clarke has told the authorities that he plans to start that process on 1 March.
There will then follow a four-month period of consultation, to give the public, local authorities and the Welsh Assembly Government the chance to make their concerns known.
Mr Price-Thomas added: "Mr Clarke is talking about a full merger by 2007 and the legislation could be agreed in time for the summer recess in July.
"There are issues in terms of geography and culture in Wales and we are making progress in that area - every local authority will have representation on the new authority - but I am concerned about the pace of the reforms."
Higher taxes
A leaked Welsh Assembly Government estimate has said that the cost to council taxpayers in the South Wales Police area could increase by 17% under a single force.
Earlier this week the all-party House of Commons Welsh affairs committee accused the Westminster Government of "rushing".
The committee also said it was not convinced that one force was the right way forward for Wales.
However, Welsh Secretary Peter Hain said that while there needed to be safeguards in respect of local policing, that a merged force was the "only serious option" to meet modern demands.
He said that the total package would ensure Welsh policing would be in a position to deal with terrorism, drugs and organised crime, as well as having the ability to react to major investigations, which stretched the resources of smaller forces.
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