Only eight of the more than 40 high school boards in the province have implemented the contracts so far. Toronto and Peel are among those boards that have still not signed-off.
School boards have until August 29 to commit to the new amended contracts.
Ontario Secondary School Teachers' Federation President Paul Elliot said there may still be some unresolved issues after the spring contract negotiations.
"They're not sure how the year is going to unfold in terms of working conditions...so we're at a point right now that something has to be done," Elliot said.
Last September, the province passed anti-strike legislation, also known as Bill 115, which allowed the government to ban strikes and imposed contracts with a two-year wage freeze
In the new year, the Ontario government used the new law to impose a contract on public and elementary secondary school teachers — a move that was later repealed. In response, high school teachers staged a month-long protest during which extracurricular activities were halted.
Elliot said the union is puzzled as to why the deals aren't in place when the boards "have an opportunity to ensure there is peace and stability in the schools.
"What's frustrating for us, the boards have been assured the funding is there at this point there's no reason for them not to go ahead and do it," he said.
The unions and government reached a deal in late March that improves the contract imposed on teachers by the McGuinty government, with improved sick day and maternity leave benefits.
$160M in additional funding
The government has made $160 million in additional funding available to the boards and Education Minister Liz Sandals said she expects them to confirm by the deadline that the deals will be in place by Sept. 30.
"We know that all of our partners in the education sector have an interest in starting the school year on a positive note," she said in a statement.
Premier Wynne echoed those calls on Thursday during a new conference at Queen's Park.
"I expect that kids will have full access to extracurricular activities this year," she said.