NDP Leader Andrea Horwath says she supports a "modest" increase to the corporate income tax rate, but wouldn't say how much.
The government says the tax currently stands at 11.5 per cent, down from 14 per cent in 2010.
Horwath says her party would also sell the province's General Motors shares — a one-time gain — and put off a proposed Toronto subway extension to Thornhill, north of the city.
She says she'd put the $3.5 billion that would be spent on that project to build a downtown relief line and the planned Scarborough subway extension.
The governing Liberals have said the current plans for improving transit in the region would cost about $2 billion a year.
They say the NDP have already promised to use money from a corporate tax hike for other purposes, such as reducing health-care wait times and eliminating the $11.3-billion budget.