Ontario Premier Dalton McGuinty says the province should prepare for its second election in less than a year after the Conservatives and NDP joined to force changes to the budget bill.

McGuinty says he would let the public decide the fate of Ontario's finances after the two opposition parties outvoted the Liberals to pass amendments to the controversial budget.

McGuinty said the Liberals could not support an amended budget and "would take it to the people in a general election" if necessary.

"It is absolutely imperative that we pass this budget. We have been fair, we have been reasonable," the premier told a news conference on Friday.

McGuinty said that the minority Liberal government has been working behind the scenes with opposition members on a number of issues, but says the budget must ultimately remain the vision of the party in power.

"Budgets are special. They are matters of fundamental confidence. They set out the direction for the government and the province to pursue. We need a toolkit to deliver on our plan of action set out in the budget," McGuinty said.

McGuinty accused NDP Leader Andrea Horwath of "joining forces with the PC" and abandoning a deal that secured the party's support for the bill. In exchange for NDP support, the budget was previously changed to include a tax on incomes over $500,000, among other concessions.

McGuinty said the budget already includes ideas from both opposition parties, but they are bent on putting their partisan spin on the spending plan. He added that the new amendments would cost the province billions of dollars.

"I cannot let this happen. This is about Ontario's economic livelihood. It is about our ability to continue steering the province in the right direction in these challenging times."

Horwath said on Thursday that she had warned McGuinty she would try for more changes before the budget was passed.

"I remain committed to passing the budget and I will do everything I can to keep my word and do exactly that," Horwath said on Friday.

Progressive Conservative Leader Tim Hudak dismissed the debate over "the Liberal/NDP budget" and said the province needed to focus on creating jobs.

"I think the people of Ontario are tired of this election posturing from the premier," he said.

Queen's Park will vote on the final budget on Wednesday.

The budget currently calls for wage freezes for 1.3 million public employees, including doctors, nurses and teachers with an aim on eliminating the $15-billion deficit by 2017-2018.

The proposed amendments include changes that limit the government's ability to privatize services and agencies, which Finance Minister Dwight Duncan said would force the premier to call for a new election.

The Liberals are one vote short of a majority government after being returned to tempered power in the election eight months ago. The premier appealed for opposition members who do not want to see another election to vote with the Liberals in support of the original budget.