Rank-and-file Liberal Democrats are being asked to revive a deal that could kick Labour out of office in Wales.
The party could overturn a decision by its national executive which wrecked a pact between the Lib Dems, Plaid Cymru and the Tories.
Lib Dem Assembly leader Mike German said: "A 'No' vote will mean there can never be anything other than a Labour administration."
The so-called rainbow coalition had a joint programme for government, called The All-Wales Accord, which Lib Dem chiefs shelved at a meeting on Wednesday night.
Plaid leader Ieuan Wyn Jones, who was on course to become First Minister, said the deal was no longer on the cards in the short term.
But if it is endorsed later it will put Rhodri Morgan, who was chosen as First Minister on Friday, in a very vulnerable position.
Labour has just 26 of the Assembly's 60 seats following the May 3 election.
Mr German said he was unaware the party's rules allowed grassroots members to call a conference when the executive met on Wednesday night.
Had he been, he could have saved his blushes when the Lib Dems came under fierce attack from Plaid and the Tories for sinking the deal on Thursday.
Some Lib Dems are opposed to any coalitions because their party failed to gain any new seats at the election. The conference is taking place at the Metropole Hotel, Llandrindod Wells, Mid Wales.
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