The Welsh Labour Party is considering striking a deal with Plaid Cymru if it fails to win a majority in the assembly election, BBC Wales has learned.
Rhodri Morgan has lacked a majority in the assembly
Prominent Labour figures have said they are considering a deal with Plaid rather than the Liberal Democrats.
It is understood Labour would be prepared to make policy concessions for Plaid support in crucial votes.
A spokesperson for Welsh Labour leader Rhodri Morgan said any talk of a deal at this stage was "utter nonsense".
Labour sources have accused the Lib Dems of "posturing and assuming they have an automatic right to be in government".
In 2000, Labour and the Lib Dems formed a coalition administration in Cardiff Bay. It lasted until the 2003 election, when Labour won a bare majority, with 30 of the 60 seats.
Labour later lost that majority, but continued to rule as a minority administration without bringing the Lib Dems back into government.
Many in Labour see the Lib Dems as natural coalition partners, and the pair have a similar partnership in the Scottish Parliament.
But it is understood that, while some senior Labour politicians believe a formal coalition with Plaid is unlikely, they would be prepared to make major policy concessions in return for the party's support in votes of confidence and on issues such as the assembly budget.
There is a recent example of Plaid coming to the aid of the minority Labour administration on the budget.
Ieuan Wyn Jones (L) in budget talks with Rhodri Morgan last year
Before Christmas, Plaid Cymru incurred the wrath of the other opposition parties when it broke ranks with them and did a deal to allow the Labour assembly government's budget to pass.
Votes of confidence
At the time Plaid leader Ieuan Wyn Jones said he had won a "major concession" on school funding.
But if this new arrangement did go ahead after the election it could be the first long-term deal between the two parties since Plaid Cymru MPs helped keep Labour Prime Minister James Callaghan in Downing Street in the late 1970s.
However, a spokesperson for Mr Morgan reacted to the BBC Wales report by saying: "Nothing has changed. Welsh Labour is going for an all-out majority in May's election.
"Any talk of coalition or informal agreements at this stage is utter nonsense and totally pre-emptive of the wishes of the people of Wales on 3 May."
Such an arrangement in Cardiff Bay would mirror what currently happens in New Zealand.
There the New Zealand Labour Party has a formal coalition with one other party and has done deals with three other parties to ensure that it does not lose any votes of confidence.
If Labour were to make such a deal, it would call into question one of the central tactics of its election campaign.
The party has repeatedly claimed that Plaid Cymru was planning to go into a "Tory-led coalition" government after next week's election.
Plaid has strenuously denied that claim.
Over recent days, the Plaid leader has refused to rule out either a deal with Labour or with the other parties, should the election fail to produce a single outright winner.
But it is understood the party is not necessarily concerned about whether this includes having Plaid ministers around the cabinet table.
BBC Wales understands that Plaid would demand major concessions from Labour at Westminster as well as in Cardiff Bay in return for its support.
This could include a commitment to a rapid expansion in the assembly's powers.