Rhode Island officials are investigating whether a former attorney general violated state lobbying rules by making appeals to his former colleagues on behalf of a Nevada gambling casino, among other corporate clients, even though he had not registered as a lobbyist.

The investigation of Patrick C. Lynch, a Democrat, who served two terms as attorney general, from 2003 to 2010, comes in response to an article in The New York Times last month that examined the surge in lobbying of state attorneys general across the country, much of it by former officials like Mr. Lynch.

Since Mr. Lynch left office, he has developed an extensive lobbying practice representing clients like payday lenders, the video game software industry, Caesars Entertainment Corporation, Comcast and Monsanto, emails obtained by The Times show.