Ontario's elementary teachers are set to resume contract talks with the government on Wednesday, but they're warning that if bargaining doesn't produce an agreement, the union will resume job action after March break.

Elementary Teachers' Federation of Ontario (ETFO) first vice-president Karen Campbell said the union — which represents 80,000 educators — has been called back to the bargaining table by a government-appointed mediator.

But Campbell warned Education Minister Stephen Lecce that the union expects his negotiators to return to talks with serious proposals.

"The minister has an opportunity now to avoid further disruptions by reaching a fair deal with ETFO prior to March 23," she said. "If these talks are unsuccessful, ETFO will resume strike action on the Monday following March break."

ETFO is the latest union to agree to return to the bargaining table after Lecce made concessions on two major issues last week, though largely affecting secondary teachers.

WATCH: ETFO's Karen Campbell says the union has been called back to the bargaining table:

ETFO set to resume contract talks with the government on Wednesday. 4:03

He offered to increase average high school class sizes from 22 last year to 23 next year — instead of the government's original target of 28 — and allow an opt-out for e-learning courses the Tories previously said would be mandatory.

The Ontario English Catholic Teachers' Association was at the bargaining table with the government for three days last week and resumed talks Monday.

The union representing teachers in the French system is also set to return to negotiations Tuesday and Wednesday.

Campbell said the call from the mediator came minutes before the start of a news conference in which the union was about to announce the resumption of rotating strikes on March 23.

"Let's be clear, this government needs to come to the table this week to demonstrate their commitment to public education," she said.

In previous talks earlier this year, ETFO said it was close to an agreement on several key issues, but that the government negotiators changed positions at the last minute.

Minutes before the start of a news conference by the Elementary Teachers' Federation of Ontario to announce its next phase of strike action, the government confirmed it is returning to the bargaining table with ETFO on Wednesday. (Lorenda Reddekopp/CBC)

Lecce called on ETFO to cease any further job action and focus on reaching an agreement in talks.

"I remain fully committed to reaching a deal that keeps students in class, provides certainty to parents, and fairness to educators," he said in a statement.

Two unions — representing high school teachers and educators in the French system — have now suspended strikes for the next few weeks, though the high school teachers say their move is because of March break.

The Ontario Secondary School Teachers' Federation hasn't formally bargained with the government since Dec. 16, though it did engage in informal exploratory talks last week.