TORONTO - Ontario Premier Dalton McGuinty has ruled out a Liberal coalition with either of his main rivals in the event no party wins a majority in Thursday's election.

In a letter obtained on Sunday, McGuinty tells Progressive Conservative Leader Tim Hudak that he won't be making any deals to form a government.

"I am running to form a Liberal government -- and only a Liberal government," McGuinty says in the letter.

"There will be no coalition with either your party or the NDP."

The latest polls indicate the Liberals and the Progressive Conservatives in a dead heat, raising the prospect of a minority government in Ontario for the first time in 26 years, with the NDP under Andrea Horwath as kingmaker.

In his letter, McGuinty says his opponents are using talk of a minority as political ammunition.

"Over the course of the weekend, you and Ms. Horwath have turned away from promoting your individual platforms and have engaged instead in trying to leverage political advantage through minority government speculation," McGuinty says.

Hudak has been accusing McGuinty of planning "backroom deals" with the New Democrats.

Earlier Sunday, he warned that Ontario could end up with a minority government coalition in which the Liberals and NDP would work together to hike taxes.

"The Liberals and the NDP: they'll increase taxes and they'll spend money on everything under the sun," Hudak said at a campaign stop Sunday.

When asked if he would work with the New Democrats if they dropped a plan to raise the corporate tax rate, Hudak indicated he wasn't interested.

"I'm in this election to win and bring change, not play 'Let's Make a Deal'," Hudak said, stressing the Liberals and NDP would cook up a deal.

On Sunday, Horwath said she planned to stay focused on talking to voters and telling them what an NDP government's priorities would be.

She was evasive when asked if she would rule out a coalition like McGuinty has done.

Instead she continued to plug a five-point plan for an NDP government's first 100 days in power.

The Liberals said McGuinty had addressed his letter only to Hudak because of the Tory leader's comments.

Hudak's strategy is reminiscent of Prime Minister Stephen Harper's, whose spring election included frequent warnings that the federal Liberals and NDP would scheme to form a coalition if his Conservatives did not get a majority.

McGuinty said voting Liberal would be the only way to ensure the "strong, stable, positive government" Ontario needs in uncertain times.