TORONTO - Ontario's integrity watchdog is being asked to investigate the possibility that illegal lobbying may have played a role in convincing the governing Liberals to allow mixed martial arts in the province.

The New Democrats made the request Friday following reports that individuals are lobbying the Liberal government without registering -- a violation of provincial laws.

Those reports also suggest that former premier David Peterson may have lobbied the government on behalf of Ultimate Fighting Championship, the party said.

Peterson has denied he did any lobbying, but NDP justice critic Peter Kormos said Ontario's integrity commissioner should investigate.

"The purpose of the Lobbyist Registration Act is to make government decision-making practices more open, transparent and accountable," Kormos wrote in an Aug. 20 letter to commissioner Lynn Morrison.

"This system is threatened when individuals skirt the rules."

The Liberal government announced last week that they would open the door to MMA in 2011.

Premier Dalton McGuinty had previously dismissed the idea of allowing the often brutal combat sport, saying it wasn't a priority for Ontario families.

The surprise move to allow MMA, as well as the Liberals' recent blessing to online gambling, have raised questions about whether McGuinty will hold on to his "Premier Dad" image.

McGuinty said he reversed course on MMA because the economy is now on the mend and his government could focus on other priorities.

Money was apparently also a factor in the flip-flop on MMA. The cash-strapped government, which is running a deficit of almost $20 billion this year and expect years of red ink, said one MMA event could attract up to 30,000 fans and generate up to $6 million in economic activity.