In a stunning about-face, Ontario Premier Kathleen Wynne will announce Friday that she will refuse to give Toronto permission to go ahead with Mayor John Tory's plan to toll the Gardiner Expressway and the Don Valley Parkway.

Ms. Wynne, who is facing an election in 2018 and riding low in the polls, is expected to break the news at an event in Richmond Hill, Ont., on Friday morning, senior city hall and provincial government sources told The Globe and Mail. She had previously suggested she would not stand in the way of the city's decision to impose tolls, approved by city council in December.

However, sources say Ms. Wynne will also announce an increase in the amount of the provincial gas tax that Ontario hands over to municipalities. One source says the new revenue could entail $170-million for Toronto to spend on public transit – close to the $200-million the city estimated the tolling plan would bring in. The gas-tax changes would also mean more revenue for municipalities across the province.

Story continues below advertisement

Globe editorial: Memo to Ontario Conservatives: John Tory is right about road tolls

Read more: The real reason house prices in Toronto are soaring

Related: Avenue of change: Meet the new kind of street coming to Toronto

Mr. Tory sold his plan for tolls, in the range of $2 a trip, as a way to make drivers in Richmond Hill and others from around Toronto pay for the city's two expressways, which are maintained by City of Toronto taxpayers and do not receive direct provincial funding.

The move is a blow to Mr. Tory, who until this disagreement appeared to have a good relationship with Ms. Wynne. Mr. Tory unveiled his toll proposal with fanfare in November, selling it as a bold plan to move the city forward. He acknowledged that he had reversed his previous position against tolls, which dated back to his run against David Miller for mayor in 2003. He is not scheduled to attend Ms. Wynne's announcement Friday, but is set to address reporters at city hall afterward.

One person close to the mayor characterized his reaction as a mixture of surprise and disappointment.

The mayor's office issued a statement Thursday night after word of the Premier's plans was reported by Steve Paikin, host of TVO's The Agenda, on Twitter.

Story continues below advertisement

"If the Ontario government has decided to deny a regulatory change requested by the overwhelming majority of City Council, the Mayor would expect the Provincial government to take serious and immediate action to address the city's transit, transportation, childcare and housing needs," the statement reads.

Shortly after Mr. Tory announced his toll plan, Ms. Wynne strongly suggested she would approve it, if city council formally asked Queen's Park for the permission it needs under the City of Toronto Act.

"If Mayor Tory and his council determine that they would like to embark on a tolling of certain roads – local roads in the city of Toronto – then we will work with them," Ms. Wynne told reporters in early December.

But later that month, in a year-end interview with media outlets, as opposition outside Toronto to the idea mounted, she made more cautious remarks. She told the CBC that she needed to "look at the timing … how big the tolls would be and all of that, and look at what options people will have."

A Queen's Park source said Ms. Wynne will cite the lack of currently available public-transit options to many commuters as a reason for turning down Mr. Tory's toll plan.

The premier has faced demands from both Progressive Conservative Leader Patrick Brown and NDP Leader Andrea Horwath to block Toronto's plan, which drivers in the swing-riding-laden 905 belt were expected to oppose vigorously.

Story continues below advertisement

Much of the toll revenue would have been eaten up by the costs of the two expressways. The Gardiner, in particular, is facing an expensive repair bill that includes rehabilitating the western portion and rebuilding the eastern leg in a slightly different position. Without the revenue stream from the tolls, it is unclear how the city could afford this work on the eastern Gardiner, raising the prospect that the controversial decision to retain this elevated expressway could be revisited.

Mr. Tory, who has championed the more expensive option of keeping the Gardiner elevated, was widely praised for proposing tolls. Now, with tolls being vetoed, Mr. Tory appears to have incurred a political risk without a compensatory benefit.

The provincial decision also raised immediate questions about fairness. Mr. Tory's former spokesperson, Amanda Galbraith, who returned to private life last month, noted on Twitter that "32 councillors [80 per cent] endorsed road tolls to pay for transit/infra[structure]. What does that say for the prov[ince's] respect for democracy?"

Some proponents of tolls argue that they not only raise revenue, but, if implemented in a way that discourages driving at peak times, can also change driver behavi‎our and reduce congestion.

Ms. Wynne has long spoken about the need for new revenue sources to build transit. Transportation Minister Steven Del Duca, who is scheduled to be with her Friday when she formally rejects the tolling plan, had said they would "carefully review" any proposal with Toronto city council support.