OAKVILLE, Ont. - Progressive Conservative Leader Tim Hudak was forced to go off-script Thursday when he was confronted by an activist at a campaign stop and pressed to weigh in on a controversial quarry project north of Toronto.

Stop the Mega Quarry's Danielle Nobrega cornered Hudak during an event with party supporters, insistently urging him to condemn the project.

The group has been protesting against Highland Companies' plan to build a massive limestone quarry near Shelburne, saying it would threaten the region's water tables and destroy prime farm land.

Hudak looked stunned to be put on the spot, but quickly recovered and said he supports the local Conservative MPP's calls for more rigorous environmental testing.

The off-the-cuff exchange stood out in a campaign marked by tightly controlled photo-ops and announcements, where media access to the Tory and Liberal leaders has been limited mostly to one availability a day.

Nobrega told reporters she's had some trouble getting close to the leaders, but "wiggled" her way up through the crowd.

Nobrega said she was hoping for a stronger commitment from the Tory leader.

"I was not happy at all because I would really like our politicians to take a firm position on this issue to allow the public to gauge and to talk about this issue, the implications of this mega-quarry," she said.

"I would like him to say firmly, 'I am against the mega-quarry and I will ensure it doesn't happen,' because that was the very question I asked," she said.

The New Democrats, who have publicly questioned the quarry plan, said they're disappointed by Hudak's mild response.

"I'm surprised that the Tories aren't coming out more strongly on this issue," said Peter Tabuns, the NDP's energy and environment critic.

"I think if you're going to protect water and agricultural land in Ontario, this is not a complicated one to think through."

Tabuns also called out the Liberals, saying they were too slow to push for an environmental assessment.

The Liberals recently announced that the site on Highway 124 will undergo an assessment, which could take up to two years.

Earlier this week, they also pledged to review the Aggregate Resources Act, the law that regulates the licensing and operations of aggregate pits and quarries across Ontario.

In an interview with CBC radio last week, Hudak blasted the Liberals for their handling of the project.

"I don't give (Premier) Dalton McGuinty any credit," he said. "They dithered and delayed on this and just moments before the election decided to do the study."

He said the company "should go back to the drawing board" and address the community's concerns.

Highland Companies, backed by a Boston hedge fund, has said any part of the 971-hectare site that's been dug up will be replaced and returned to an arable state.