TORONTO - The chances of Ontario voters returning to the polls for the second time in six months are slight, even though the minority Liberals have yet to strike a budget deal with the NDP to avert another election, Premier Dalton McGuinty said Tuesday.

"There's a possibility that both parties -- both opposition parties -- decide that their first choice is an unnecessary, expensive election to be held within six months from the time we had the last one," he said during a campaign-style stop at the Toronto office of eReader maker Kobo.

"I think it's a remote possibility. We'll do everything we can to ensure that that does not unfold, but it is there nevertheless."

The Opposition Conservatives have already said they'll vote against the budget, so McGuinty must woo the New Democrats for his government to survive.

The premier said he's still optimistic that he'll reach a budget deal with the NDP to avoid defeat on April 24, when the budget motion will be put to a vote in the legislature.

Despite his conciliatory tone, the Liberals and New Democrats seem intent on pushing each other's buttons over the budget.

One of the New Democrats' key demands is to hike taxes for the wealthy by introducing a two percentage point surtax on incomes over $500,000.

That puts McGuinty in a tight spot, because he's repeatedly promised not to raise taxes to eliminate the deficit, despite doing so after the Liberals were elected in 2003.

The NDP claim the tax hike will bring in enough money to offset raising welfare rates, saving daycare spaces and putting more cash into community and home care. But the Liberals insist the NDP's demands -- which also include removing the provincial portion of the HST from home heating bills -- is too expensive for a province that must slay a $15.2-billion deficit by 2017.

The NDP are indicating they're prepared to "give a little" on their demands, McGuinty said, but he added he needs to know where they stand on a wage freeze for workers in the broader public sector.

"We cannot possibly balance this budget unless we hit the pause button when it comes to public sector pay," he said, adding the freeze will save $6 billion over three years.

"And I have yet to hear in a definitive way from the NDP where they stand on this issue. We just can't get there unless we freeze that pay."

The Liberals warned in the March budget that they're prepared to legislate the freeze if all other options fail, but the threat isn't in the actual budget bill because it doesn't require a legislative change.

The wage freeze is a sensitive issue for the left-leaning New Democrats, with some supporters demanding that the union-backed party call McGuinty's bluff and vote against the budget if he doesn't withdraw the threat.

NDP Leader Andrea Horwath said she's made it clear for a long time that a wage freeze can only be found at the bargaining table, and McGuinty knows it.

Even his own austerity expert, economist Don Drummond, said a legislated freeze doesn't work, she added.

"I don't think that putting some kind of game of brinkmanship like that on the table is the wise thing to do at this point, and I would certainly hope that that's not what the premier is doing," Horwath said.

The Liberals' hardball approach with unions has already raised the ire of teachers and doctors, who have taken their fight public.

On Tuesday, the Ontario Secondary School Teachers' Federation announced it's launching a legal challenge against the government "regarding concerns related to the collective bargaining process." The challenge is expected to be filed with the Ontario Labour Relations Board this week.

If a budget deal isn't reached this week, the NDP could buy more time by supporting the budget or abstaining from the April 24 vote. That would allow them to put off their final decision until a second confidence vote on the budget legislation is called.

But with all three parties still mired in campaign debts, there appears to be little appetite for another election.