Ontario's Liberal government has secretly offered contract extensions to almost all of the key education unions in a move that would buy the ruling party support from teachers and a degree of labour peace during an election.

Extensions would mean opening the treasury to ensure most public high school teachers, elementary teachers and education workers do not strike before the vote expected in the spring of 2018. The province is even willing to consider rewriting the law that governs bargaining to extend the contract.

Premier Kathleen Wynne and Education Minister Mitzie Hunter dodged questions about the possible extensions on Monday.

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Last week, The Globe and Mail revealed that the Liberals had offered the extension to the Ontario Secondary School Teachers' Federation. Asked on Monday how many other unions had received similar offers, the Premier said she did not know.

"I can't tell you chapter-and-verse exactly who has had which conversations, but there are conversations going on with many public-sector employees," she said at an unrelated announcement.

Ms. Hunter said she did not know how many unions had received offers, and suggested reporters should ask the unions. Neither explained why they did not know.

"That information I don't have. You can talk to the other labour partners about that," Ms. Hunter said.

In a later statement to The Globe and Mail, she said contract extensions have been raised with unions. Ms. Hunter's spokesman also confirmed contract extensions have been offered to all unions that were part of a lawsuit against the government over Bill 115, a 2012 piece of legislation that imposed contracts on education unions and suspended their right to strike.

OSSTF, the Elementary Teachers' Federation of Ontario and the Canadian Union of Public Employees, among others, won a court ruling earlier this year and the law was deemed unconstitutional. These unions are discussing compensation with the province; the contract extension is one option. The Ontario English Catholic Teachers' Association was not part of the lawsuit, and a spokesperson said on Monday it has not been offered an extension.

A memo sent to OSSTF members on Friday, a copy of which was obtained by The Globe, said the government approached the union about an extension, and that the union planned to draw up a brief on issues that should be pursued. OSSTF president Paul Elliott confirmed the union was "exploring the possibility" of an extension.

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A spokeswoman for ETFO reached on Monday declined to comment on the discussions. Andrea Addario, a spokeswoman for CUPE, said the union was approached about an extension and is reviewing its options.

All collective agreements with education workers in the province expire next August.

During the previous round of bargaining, the province insisted all labour deals be "net zero," meaning something had to offset the cost of raises. That led to tough negotiations during which the OSSTF unleashed strikes in the Toronto area and Northern Ontario, and the government legislated the teachers back to work.

Last week, Ms. Wynne said she is ready to loosen the purse strings for the next round of talks with public-sector unions.

Education observers point out that the school boards' collective bargaining legislation does not allow contracts to be extended.

Ms. Hunter said in a statement the parties are talking about potential changes to the legislation.

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School boards say they have not been contacted.

Laurie French, president of the Ontario Public School Boards' Association, said extending the contract requires input and ratification from her group.

"Now that there is clarity of the unions' interest in exploring an extension of the collective agreement, OPSBA and the other school board associations have an expectation that they be contacted by the government to be included in the discussions," Ms. French said.