TORONTO - Ontario Premier Dalton McGuinty refused Monday to put a price tag on his late-in-the-game pledge to scrap a gas-fired power plant, as he was dogged by what is quickly becoming a hot-button election issue.

The Liberals quietly pledged this weekend to cancel construction of the 280-megawatt natural gas-powered facility in Mississauga, Ont.

It's up to voters to decide whether they want the Liberals to act on that plan, McGuinty said Monday, but he wouldn't attach a price tag to what it would cost to halt construction and move the plant elsewhere.

When asked if he could give taxpayers a ballpark estimate, McGuinty replied, "no."

"That's the subject of continuing conversation and we'll work that out over some time," he said.

McGuinty was also asked if he could give some idea as to where the plant might be relocated.

"Nope," he said.

Construction has already begun on the plant site and major equipment has been ordered.

The government spiked a similar, 975-megawatt project in neighbouring Oakville almost a year ago, but McGuinty couldn't attach a cost to that, either.

"It's still the subject of continuing conversation," McGuinty said.

In October 2010, after the government suddenly pulled the plug on the Oakville plant, McGuinty said he wasn't aware of the specifics of the contract with TransCanada Corp., which won the bid to build the $1.2-billion plant, and couldn't say how much it would cost to break the deal.

New Democrat Peter Tabuns said the Liberals realize it was a mistake to try to put the Mississauga plant there in the first place and are now scrambling with days left until the Oct. 6 election.

"I saw the polling this weekend," he said. "They're having real problems in Mississauga. They're trying to save the seats. They made a decision on that basis. That's the most reasonable conclusion."

The local community has opposed the project since it was announced six years ago, but McGuinty says a changing population and lower demand for power prompted his decision now.

"There's never a wrong time to do the right thing," McGuinty said. "I've always said that we're going to keep an open mind and we'll keep listening to people, and we've listened and now we've acted."

Both the NDP and the Tories say they wouldn't have tried to put a gas plant there in the first place.

"We've never supported this idea of forcing gas plants into unwilling host communities in such an arbitrary fashion," Progressive Conservative Leader Tim Hudak said in Waterloo, Ont.

"Clearly their plan is to put a gas plant somewhere in the west (Greater Toronto Area). I just wish Dalton McGuinty were honest about it and say if he is moving, where is he moving it to?"

With about one week and a half to go in the election campaign and the televised leaders' debate set for Tuesday night, the issue isn't likely to fade soon. The Liberals and Conservatives released duelling "open letters" Monday.

In his letter, Hudak demanded McGuinty tell voters the cost and potential new locations for the plant before election day. The Liberals shot back in the afternoon with their own letter to Hudak, saying he is misleading voters when he calls the deal cancelled instead of relocated.

The Liberals' also quoted the head of the group that led the charge against the power plant as criticizing the Conservatives for not taking a position on the plant until after the Liberal announcement.