TORONTO -- Put it in writing, please.

That's Premier Dalton McGuinty's response to NDP Leader Andrea Horwath's request for emergency talks on passing the provincial budget and averting an unpopular summer election.

"Specifically, I ask you to commit yourself and your party, in writing, to not alter the intent or block passage of any more schedules of the budget bill," McGuinty said in a letter to Horwath sent Sunday.

"And, of course, I will also need your written assurance that you will not block passage of the budget bill in the legislature."

McGuinty said in the letter he had twice come to what he thought were deals with the New Democrats to secure their support for his budget -- which would need votes from the third party to pass the minority legislature.

Neither deal was in writing, though, and McGuinty told Horwath he was "disappointed" to see her party still pushing for changes in committee, despite winning an end to corporate tax cuts, a high income surtax, and improvements to welfare and disability benefits.

"On the basis of those two agreements, I believed -- and more importantly, Ontario families clearly understood -- the budget bill would pass," McGuinty wrote.

"But to my surprise and disappointment, your party began to dismantle the very budget bill you personally agreed to see pass. Several key provisions were defeated on Thursday and your party has given notice that many more are at risk tomorrow (Monday) and Tuesday."

There was no immediate response to the letter from Horwath, who appealed Saturday to both McGuinty and Progressive Conservative Leader Tim Hudak to call her.

A vote on the budget is set for Wednesday. Failure to pass it would mean an election as early as July 19, nine months after McGuinty won a third term -- just one seat short of a majority.

Horwath replied she's now more convinced that a snap election call can be avoided this week, while still passing an "improved" budget.

"I am glad the premier has changed his tune of the last few days and is no longer making election threats," Horwath said.

Horwath added she remains committed to making changes to the budget at committee but does not disclose whether she accepts McGuinty's terms.