The Progressive Conservative party continues to enjoy a commanding lead ahead of the June 7 provincial election while Kathleen Wynne and the Liberals have dropped to third place behind the NDP, a new poll has found.

The Mainstreet Research poll of 2,534 Ontario voters found that 42.3 per cent of decided or leaning voters plan to cast a ballot for the Tories while 28.4 per cent say they will vote NDP and 22.1 per cent say they will vote Liberal. About 5.4 per cent said that they will vote for the Green party.

It is the first time that the NDP have leapfrogged the Liberals in a Mainstreet Research poll and comes just one day after PC Leader Doug Ford repeatedly attacked Andrea Horwath’s party prior to a leaders debate in Parry Sound.

At the time, Ford dismissed suggestions that he was targeting the NDP because he perceived them as a threat.

"We've been noting a very significant surge in NDP support among leaning voters and second choices for the past few weeks. Today as we begin our province-wide polling for the election period, we see a very significant shift in voter intentions from our final pre-election poll of April 30th,” Mainstreet Research President and CEO Quito Maggi said in a press release. "While the topline numbers are downright frightening for the incumbent Liberals, the regional numbers reveal even worse news for Premier Wynne. While the PCs had a bad week and dipped in support, they maintain a very substantial lead."

Liberals now trailing in Toronto

Overall, NDP support was up 7.1 per cent among decided voters from the last poll on April 30th while Liberal support was down 6.1 per cent and Tory support was down 2.6 per cent. Support for the Green party, meanwhile, was up 1.4 per cent.

Broken down by region, things seem even more bleak for the Liberals, though. In their usual stronghold of Toronto they currently trail the Tories by about six points among decided voters (36.1 per cent to 30.3 per cent) and in the 905 region outside the city they are languishing in third place with the support of 23.1 per cent of decided or leaning voters compared to 25 per cent for the NDP and 44.9 per cent for the Tories. Mainstreet Research said that could point to a “potential sweep” of the 905 for Doug Ford should the trend hold.

Meanwhile, in both northern Ontario and southwestern Ontario, the PCs enjoy commanding leads with the support of 45.1 and 45.8 per cent of voters, respectively.

The NDP are safely in second in both regions with the support of 32.5 and 31.5 per cent of voters.

"These regional numbers are pointing to a very challenging path for Kathleen Wynne. But things could get worse for the Liberals in the days ahead if progressive voters decide to vote NDP to stop Doug Ford from becoming Premier,” Maggi said in the press release. "A lot can change in the campaign because things have changed in the last few months. But if the election were held today, we would see a PC majority, an NDP opposition, and the Liberals struggling to get their seat count to double digits."

The poll is considered accurate to within 1.95 percentage points, 18 times out of 20.