The current Liberal government has what amounts to a one seat minority. That means that the government can be defeated if the opposition parties gang up and declare they have "no confidence" in the government. That generally happens over substantial matters that deal with money, in this case it was the province's 2012-2013 budget that was presented back in late March 2012. The Ontario legislature gets to discuss and vote on the budget provisions as if it were a bill.
Of the two opposition parties, the Progressive Conservatives (oxymoron?), were against the budget from the outset, and so-called socialist New Democratic Party (NDP) carried the deciding votes. The NDP decided to do some arm twisting, and managed to add an additional tax on the wealthy along with some other minor tweaks.
The budget was supposed to address the growing provincial deficit and debt, something that the Liberals have exacerbated over the past 8 years. Now they wanted to fix it, and this budget was designed to balance the books in five years. Not the debt, mind you, it would continue to grow over those five years, just stop spending more than you bring in, that was the goal. Of course eliminating the deficit in Ontario depends on continued growth of the economy and no surprise shocks that may negatively impact the province. The latter is about as likely as the sun NOT rising tomorrow morning. But I am no expert. Why not watch and listen to an expert who thinks the Liberal plan is flawed and unrealistic. Not only that, but Niels Veldhuis has a better idea: