Plaid Cymru has reacted angrily to claims by the Welsh secretary that a referendum on giving the assembly full law-making powers would be defeated.
The party want Welsh Labour to distance itself from Peter Hain's remarks that there was no consensus on a vote.
Plaid Cymru MP Adam Price said the two parties' coalition was under threat unless Welsh Labour gave reassurances.
A referendum within four years was part of the One Wales deal which led to the Labour-Plaid assembly government.
Adam Price MP spoke out after Peter Hain MP told BBC Radio Wales' Sunday Edition programme that a referendum could not be won by 2011.
He said there was no consensus on a vote and could not see it happening over the four years of this assembly.
He spoke after it was announced that retired diplomat Sir Emyr Jones Parry was to become chair of commission on a referendum by 2011.
But Adam Price said his statements were a cause for concern because the issue was one of the main elements of the agreement of a coalition assembly government.
"It's a very confusing picture with Peter Hain almost directly contradicting First Minister Rhodri Morgan that there would be a referendum by 2011," said Mr Price.
"What we want is a confirmation from Welsh Labour that Peter Hain was not speaking for them.
"The Secretary of State is not just a back bench MP, he is a member of the cabinet and we have to get UK agreement for a referendum.
"We need him to clarify his position or withdraw his comments or for Rhodri Morgan to make it clear that he [Peter Hain] does not speak for Welsh Labour."
He said he feared for the future of the coalition unless assurances from Welsh Labour that they were not "reneging" on the issue of the referendum were made.
Labour MP Paul Flynn also spoke out about Peter Hain describing him as being "pessimistic" about the issue.
He said there was a "feeling from MPs of all parties that they don't want to lose power and they see power flowing down the M4 to Cardiff.
"The 'One Wales' agreement is more important than the opinion of one MP," he said.
"I think the process of devolution is accelerating and I believe Peter Hain is being pessimistic and he is wrong.
"I believe a referendum would be won handsomely in four years," he added.