KITCHENER, Ont. - Ontario's premier says the only unregistered lobbyists bending his ear on mixed martial arts are his children.

Dalton McGuinty is facing opposition allegations that illegal lobbying played a role in his decision to allow MMA fights in the province.

The NDP has asked Ontario's integrity watchdog to investigate, and speaking Monday in Kitchener, Ont., McGuinty said he is willing to put the decision under scrutiny.

"I would welcome any such inquiries on the part of the integrity commissioner or anybody else, because I am absolutely confident that nothing untoward took place," he said.

NDP justice critic Peter Kormos wrote two letters to commissioner Lynn Morrison about whether unregistered lobbying may be going on.

The Ontario Liberal Party is advertising a $250-a-ticket fundraiser Oct. 19 hosted by former premier David Peterson and his colleague Noble Chummar, who is a registered lobbyist for Ultimate Fighting Championship.

The close relationship between UFC, Chummar and Peterson raises questions given the government is developing regulations around mixed martial arts, Kormos has said.

Peterson has called the suggestions of wrongdoing "scurrilous" and "factually incorrect."

The Liberal government announced two weeks ago that they would open the door to MMA in 2011 after McGuinty had dismissed the idea of allowing the often brutal combat sport, saying it wasn't a priority for Ontario families.

But McGuinty joked Monday that he had unregistered lobbyists in his own family.

"Perhaps those who ought to have been registered as lobbyists would be my three sons and my one daughter, who have been lobbying on this incessantly for a long time," he said.

Money was apparently also a factor in the flip-flop on MMA.

The cash-strapped government, which ran a deficit of $19.3 billion in the last fiscal year and expects years of red ink, said one MMA event could attract up to 30,000 fans and generate up to $6 million in economic activity.

"When I was originally asked about whether we should have mixed martial arts in Ontario I made it clear that was not a priority at that time," McGuinty said.

With the economic recovery taking hold in the province the government had more time to consider other things that "Ontarians had been asking us about, including things like mixed martial arts," he added.

"We thought that it was appropriate that Ontarians have the choice."