Plaid Cymru has confirmed for the first time that it's in talks with Labour over the Welsh government's budget.
The party says it has made a "public offer" to Labour and wants to see more cash for councils and the health service before it makes an agreement.
Plaid leader Rhun ap Iorwerth said the Welsh government's existing plans, announced in October, would "hit our public services hard" .
The Welsh government was asked for comment.
Plaid's leader accused the First Minister, Eluned Morgan, of not knowing what was going on with the budget talks as the two clashed in the Senedd on Tuesday.
At the last budget Labour ministers were able to rely on the single vote of Jane Dodds, the Welsh Liberal Democrat leader, to get their spending plans through a Senedd vote.
But Plaid's victory in the Caerphilly by-election has meant that Labour needs two extra votes to get next January's budget through the Senedd.
To find a deal, ministers have already spoken to the Welsh Conservatives, Dodds and independent MS Russell George.
Although Plaid has struck budget agreements with Labour in the past, it joined the Conservatives in voting against the last set of spending plans.
Last October the Finance Secretary, Mark Drakeford, released a draft budget which saw each department funds rise by around 2% each.
But the figure is expected to change, because the budget left hundreds of millions unallocated and available for discussions with opposition parties on how they might want to spend it.
There were warnings that if the budget did not change, NHS organisations and councils may need to cut services and jobs, when costs are rising at different rates in different services.
Drakeford has said he is open to providing extra money to both services through the budget talks.
A Plaid source confirmed that the party's finance spokesperson, Heledd Fychan, and Drakeford had met.
They said the figure of extra cash to work with was not precisely known - it was reported to be £230m for day to day services in early November.
Eluned Morgan came under fire from Rhun ap Iorwerth in the Senedd on Tuesday, claiming that thousands of council jobs were on the brink.
"A grim picture emerges of public services teetering on the edge," he said, saying that the spending increase for the NHS amounts to 0.3% in real terms.
Morgan told the Senedd on Tuesday that "our door is open" to Plaid.
"We have invited you to talk to us about the budget... you could help to fix that."
In response, Ap Iorwerth told the first minister to "keep her fingers on the button and keep up with what's going on".
"Plaid Cymru is, first minister, ready to get Wales out of the hole made by Labour," he said.
A later statement from him accused Morgan of being "seemingly unaware that initial discussions had already taken place to understand the budgetary situation".
Ap Iorwerth said Morgan had "completely ignored the public offer by Plaid Cymru to allow a budget settlement to save the NHS and councils from the harm of Labour's original budget tabled".