The premier says all parties are expected to follow the rules.
Kathleen Wynne made the comments as the Ontario Liberals accuse the NDP of breaking campaigning finance laws with a billboard in the Niagara Falls by-election.
Wynne says she not only expects here party to follow the rules but everyone else as well.
She was at a by-election event in Thornhill when asked about the advertisement.
Liberals claim the large billboards featuring NDP Niagara-candidate Wayne Gates and NDP leader Andrea Horwath violate the Elections Finance Act.
The new billboard was erected during an advertising blackout period.