The Ontario Secondary School Teachers' Federation now says its members must stop leading and participating in any extracurricular activities starting next Monday.
A failure to do so could result in a fine of up to $500.
This news comes shortly before parents and guardians find out whether the elementary school teachers union has voted to support a strike.
A province-wide vote wraps up Tuesday night as teachers decide if they agree to a one-day political protest if the Ontario government chooses to enforce an end to legal strike actions through Bill 115.
“Last night we had about 40,000 of our members out of 76,000 who had voted,” said Sam Hammond, president of Elementary Teachers' Federation of Ontario.
“We wanted to ensure that all of our members had ample time to vote.”
The law, that was passed earlier this fall, imposes wage freezes and limits teacher’s unions’ ability to strike.
Education Minister Laurel Broten has said she will stop any strike actions and blames the union leaders, not teachers, for the standoff.