McGuinty signed on to the lobbyist registry in late August to act on behalf of Kitchener-based Desire2Learn, which develops educational software.
Treasury Board President Deb Matthews says McGuinty waited 18 months after leaving the premier's office to become a registered lobbyist, when the rules state he only had to wait 12 months.
Matthews says what's important is the principle of transparency, and as long as people know McGuinty is a lobbyist his transactions with government will get the appropriate scrutiny.
Education Minister Liz Sandals says McGuinty has followed the rules and has every right to lobby his former cabinet colleagues on behalf of a private company.
Sandals says she hasn't met with McGuinty since he joined the province's lobbyists registry.