The Ontario Secondary School Teachers' Federation says bargaining unit presidents voted 96 per cent in favour of the tentative deal at a meeting Thursday in Toronto.
Full details of the agreement — which will be voted on by teachers between now and April 18 — were not released.
Government sources have said younger high school teachers will be given a much better payout for their banked sick days under the agreement with the minority Liberal government.
The sources said teachers with less than 10 years on the job will get 25 cents on every dollar for sick days they banked, compared with 10 cents under existing agreements.
The union and Premier Kathleen Wynne have insisted the updated tentative agreement would not cost the province any additional money.
OSSTF Ken Coran said Thursday that the union worked within the government's fiscal parameters and came up with "a way of doing business slightly differently."
"We have come up with different ways of restructuring some components of the imposed working conditions that our members will have a chance to vote on," Coran said.
Education Minister Liz Sandals said working within existing education funding wasn't an impediment to reaching the agreement in principle.
"It was a catalyst for innovative thinking, collaborative problem-solving and the renewal of our proud partnership with Ontario's public high school teachers," Sandals said in a statement.
Bill 115 imposed contracts on 140,000 public elementary and high school teachers Jan. 1 and implemented a two-year wage freeze, also eliminated their ability to bank months worth of sick time to be cashed out on retirement.
It also wiped out any banked sick days for teachers with less than 10 years of experience, and cut the number of sick days going forward in half to 10 a year.
Teachers in the Catholic and francophone systems accepted the wage-freeze contracts without having them imposed by the province.