TORONTO -- Premier Kathleen Wynne is dismissing opposition party complaints that the Liberal candidate in the Scarborough-Rouge River byelection had an unfair advantage by knowing when the vote would be called.

Liberal candidate Piragal Thiru sent out an email Wednesday announcing the byelection several minutes before the government's official news release saying the vote would be held Sept. 1.

The governing party quickly apologized in a brief news release.

"This was the case of an eager local campaign that should have waited two minutes until the government release was posted," it said.

The New Democrats filed a complaint with Elections Ontario asking for an investigation into what they said looks like collusion between the premier's office and the Liberal campaign.

Wynne called it a "two minute mistake" which she attributed to "an overly eager campaign," but said there was really no advantage for Thiru because everyone expected the byelection call to come Wednesday.

"The reality is everyone knew that there was going to be an announcement and all the candidates had been nominated for all the parties, and I don't think it was a real surprise to anyone," Wynne told the Canadian Press Friday in an interview.

"We have apologized for that timing."

Economic Development Minister Brad Duguid insisted "it's hardly a major issue" to see a Liberal campaign press release just minutes ahead of the official byelection announcement.

"We do regret there if there is a convention with regard to these items that that convention wasn't followed," he said.

Wynne and Duguid said they don't see how the NDP and Progressive Conservatives can claim the Liberal candidate was given an unfair advantage.

NDP house leader Gilles Bisson said the only way for the Liberal campaign to know the date ahead of time was to be given the information, and he believes that is ultimately Wynne's responsibility. It suggests Wynne is more interested in winning the byelection than the conduct of a fair election, he added.

"I am requesting that Elections Ontario investigate an apparent violation of the Election Act, and a clear violation of electoral convention and the principle of electoral fairness, by the premier," Bisson wrote in a letter to chief electoral officer Greg Essensa. "In addition to giving their campaign an unfair advantage, this undermines Ontarians' faith that elections are being conducted fairly."

Progressive Conservative critic Monte McNaughton said it was "irresponsible" of the government to be so dismissive of the opposition parties' concerns about the Liberal candidate having advance knowledge of the timing of the byelection.

"We've unfortunately grown accustomed to this government putting the Liberal Party ahead of the best interests of the people of the province," he said. "Voters in Scarborough have a chance to send a message to Kathleen Wynne and the Liberal government that we want to clean things up at Queen's Park.

Wynne still hasn't set a date for the Ottawa-Vanier riding, which was left vacant when former attorney general Madeleine Meilleur resigned in June.