Plaid-Liberal Democrat deal on future budget talks
Plaid Cymru and the Liberal Democrats have agreed to co-operate with each other in future negotiations over the Welsh government's budget.
Party leaders Leanne Wood and Kirsty Williams announced the deal at a joint news conference.
They said that in future Welsh ministers would have to negotiate with one team representing both parties.
They said the economy, education and health would be their priorities when talks start in the autumn.
The Welsh government has had a fairly easy time of it over the past two years when it comes to securing a majority for the budget in the assembly.
By playing Plaid and the Liberal Democrats off against each other Labour has been able to cut deals which, while not insignificant in themselves, haven't altered the broad thrust of policy.
Even better from First Minister Carwyn Jones' point of view his concessions - the so-called "pupil premium" for the Liberal Democrats and more apprenticeships for Plaid - were both policies that were popular with Labour AMs and supporters.
By presenting a united front Plaid and the Lib Dems will hope to secure far larger concessions with an increased focus on spending on education and economic development.
The deal suggests that the second half of this assembly term could prove more difficult for the government particularly if the cooperation between the two parties spreads to other aspects of the assembly's work.
With 30 out of the 60 seats in the assembly chamber, Labour needs support from one of the other parties to get its budgets passed.
Last year Plaid Cymru abstained in the vote on the 2013/14 budget in return for extra spending on apprenticeships and funding to create the new Menai Science Park.
On Tuesday the Plaid and Lib Dem leaders told journalists in Cardiff Bay that they would refuse to negotiate with the Welsh government unless both their parties were at the table.
Ms Wood said: "Plaid Cymru is determined to deliver the best deal for the people of Wales.
"Working together with the Liberal Democrats will put us in a strong bargaining position to force the government to take action that will boost the economy, address its failures on health, and improve standards in our schools."
Ms Williams also highlighted the economy, health and education as her priorities.
"I am pleased that we are able to work with Plaid Cymru to try and secure a budget that will serve the whole of Wales," she said.
"By working together we hope to get the most for the people of Wales."
Reacting to the announcement, a Conservative spokesman said they were concerned the other three parties in the assembly were not prioritising the health budget.
"With unwanted NHS reform on-going and hospitals being downgraded, politicians must look carefully at their actions", the spokesman said.
"Welsh Conservatives do not believe patients should travel further for treatment - and we remain the only party committed to protecting the health budget."