TORONTO -- Ontario's high school teachers will be in the classroom on the first day of school, their union leader said Thursday, but they are gearing up for a fight.

Contracts for teachers and education workers in the province expire on Aug. 31, but bargaining for a new deal is still in its early stages. The Ontario Secondary School Teachers' Federation is going to the Ontario Labour Relations Board on Aug. 22 to determine what issues should be bargained centrally, and what should be deal with at local tables.

OSSTF president Harvey Bischof said he doesn't expect substantive talks to get underway until mid-to-late September, and would not speculate about possible future job action.

"We will be at work on the first day of school," Bischof said in a speech to a union conference. "In spite of already serious staffing losses, we will do everything we can to provide students with the best possible education."

Negotiations are happening at the same time as students will head back to school with fewer teachers because the government is increasing class sizes, which will mean fewer course offerings and extracurricular activities for students, Bischof said Thursday.

Legislation that would cap public sector wage increases at one per cent a year also looms, he noted.

"The government at Queen's Park has declared war on one of the best education systems in the world," he said in his speech. "We have seen hostile governments come and go, but we are still here."

Education Minister Stephen Lecce said he is "cautiously optimistic" that a deal can be reached.

"As certain union leaders are preparing for battle, as was his words, I and the ministry and this government, the premier, is preparing for the first day of class," he said. "I want to make sure that we continue to focus and negotiate at the table in good faith."

The president of the Elementary Teachers' Federation of Ontario also delivered a speech Thursday, and said so far his union has found the bargaining process to be respectful.

"Unfortunately, this is probably the calm before the storm. Already, we are seeing clouds on the horizon," said Sam Hammond, referencing the same legislation as Bischof. The union is considering options to respond to the bill if it is passed in the fall, he said.

The Canadian Union of Public Employees, which represents 55,000 education workers, asked for a conciliator to be involved with its talks with the province.

The government announced earlier this year that high school class sizes will increase from an average of 22 to 28 over four years, and average class sizes for Grades 4 to 8 will increase by one student per classroom. The government has said that will mean 3,475 fewer teachers in the system over four years, achieved by not filling vacancies when teachers quit or retire.

Lecce said teachers who received layoff notices in the spring are being rehired, as the government predicted, thanks to a $1.6-billion "attrition protection fund" it offered to school boards.

But Bischof said some layoffs are going forward, and he will know more concrete numbers in September.