The Elementary Teachers' Federation of Ontario says it's going back to court after failing to agree with the province on a remedy for the government's violation of education workers' rights.
Ontario is on the hook for more than $100 million to compensate teachers and education workers for violating their rights in 2012 by imposing contracts on them.
Several unions took the government to court over the legislation known as Bill 115, which froze some of their wages and limited their ability to strike.
The judge sided with the unions but left the question of a remedy up to the government and unions to decide.
Deals have so far been struck to pay the Canadian Union of Public Employees, the Ontario Secondary School Teachers' Federation and the Ontario Public Service Employees Union.