First Minister Rhodri Morgan has been urged by Labour MPs to resume talks with the Liberal Democrats on forming a coalition Welsh Assembly Government.
Rhodri Morgan needs support from another party to stay in power
Mr Morgan has met Welsh Labour MPs amid their growing unease about the prospect of a deal with Plaid Cymru.
Labour talks with Plaid appear to be close to reaching a conclusion.
But Wayne David, secretary of the Welsh Labour MPs, stressed party unity was essential and they would prefer "a meaningful dialogue" with Lib Dems.
A week ago Welsh MPs backed Mr Morgan in the negotiations but said they wanted to be consulted at every stage.
Mr Morgan has now held a second meeting with MPs, with many expressing strong reservations about a Plaid deal.
The prospect of a referendum on full law-making powers for the assembly is one of the disputed issues.
Caerphilly MP Mr David said: "There was great deal of discussion about that and we don't want to be locked into a situation whereby the political landscape in Wales is dominated over the next few years by a referendum"
Earlier, a senior backbencher had said: "There is rapidly growing unease here about the deal with the nats (nationalists).
"It was never popular but there are only two people (MPs) who have something positive to say about it."
One of the disputed issues is the prospect of a referendum to give the assembly Scottish-style law-making powers and a convention of the "great and the good" before any vote.
In an attempt to reassure Labour MPs, Secretary of State Peter Hain is understood to be promoting the idea that Plaid and Labour AMs and MPs should agree the terms of reference and membership of any convention.
Mr Hain believes this would act as "a political reality check" on any moves towards a referendum.
Plaid leader Ieuan Wyn Jones is to meet his party members across Wales from the end of the week to explain the choice he believes Plaid should make.
HOW THE PARTIES STAND
Labour: 26 seats
Plaid Cymru: 15
Lib Dem: 6
Plaid could also chose to form an alliance with the Tories and Lib Dems.
Mr Jones has written to Plaid members inviting them to attend one of seven meetings being held across the country.
He says this is "the beginning of a very historically important time in the assembly - a time that could see Plaid Cymru in government - a party that is ready and keen to ensure the best for Wales."
Plaid AMs are expected to chose which of the two deals they favour within days, with the party's executive then expected to agree to put the proposal to a special conference on 7 July.
A Labour special conference is due to be held on the day before to consider any deal with the rival party. Mr Morgan is currently heading a minority Welsh Assembly Government, after Labour was left five seat short of a majority in the May 3 election.
Meanwhile Lib Dem AMs agreed on Tuesday night to give Plaid Cymru "a bit longer" to "make up their minds".
A party official confirmed that the AMs had also agreed on a strategy should its preferred deal with Plaid and the Conservatives collapse.
Lib Dem AM Peter Black wrote on his blog: "We were united however in agreeing that Mike German should approach Rhodri Morgan if the so-called rainbow coalition ceased to be an option.
"An urgent national executive meeting will be called to endorse this action if necessary".
The Lib Dems suspended talks with Labour five weeks ago to concentrate on negotiating a deal with Plaid and the Tories.
Conservatives have claimed the credit for the first defeat on the minority Labour assembly government since the election.
They said other opposition parties united around a Tory motion calling for "a series of ambitious measures to tackle climate change."
Among the Tory proposal were for a programme to achieve annual carbon-equivalent emissions reductions of 3% per year by 2011.