High school teachers across the province have voted 95% in favour of strike action.
The Ontario Secondary School Teachers' Federation (OSSTF) says the result gives an "overwhelming" mandate to take job action if necessary.
OSSTF also represents education workers who voted 92% in favour of taking strike action.
Workers are already in a legal strike position as of Monday — it is required to give five days notice before a strike, which has not yet happened.
Elementary teachers are set to start a work-to-rule campaign on Nov. 26 that they say will target ministry and school board administrative tasks but won't affect student learning.
Catholic teachers voted 97% in favour of a strike if necessary, although they are not yet in a legal strike position, while negotiations between the province and French teachers continue.
Meanwhile, Ontario's education minister says the unions should consider mediation instead of escalating their labour dispute.
Stephen Lecce says having an independent third party would help the two sides reach deals on key issues such as compensation.
— With files from The Canadian Press