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Artists Against Fracking said neither the group nor supporters Yoko Ono or Sean Lennon have been told to register as lobbyists in their campaign against gas drilling in New York, but will if necessary to continue their work.

A good-government advocate and two lobbying experts said the state should review whether Artists Against Fracking and its supporter-celebrities should be registered as lobbyists.

The group and nearly 200 entertainers connected with it aren't currently registered lobbyists, a search by The Associated Press of the database of the state Joint Commission on Public Ethics shows.

Registration would require disclosure of how much money the group has raised and how it's been spent — a measure intended as a way for the public to know who is influencing public policy.

David Fenton, a spokesman for the group, said Monday it would have no objection if required to register.

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"Yoko and Sean, as true with many New Yorkers, have expressed concerns about fracking, participated in the submission of comments to the Department of Environmental Conservation, and visited Albany with their own resources," Fenton said. "As such, neither Yoko, Sean, nor their Artists Against Fracking endeavor have been required to be registered lobbyists. If there is a need to register, of course, that will occur."

Over the years, several celebrities or their groups have been required to register as lobbyists. But whether celebrities must register hinges on specific circumstances. The line between lobbying and free speech isn't bright or clear.

Under state law, a lobbyist is defined as any person or organization "employed, retained" in "any attempt to influence the passage or defeat of any legislation ... or approval or disapproval of any legislation by the governor." That can include nonprofit groups and their unpaid advocates.

The activists, among them actors Mark Ruffalo and Susan Sarandon, are trying to protect the environment from hydraulic fracturing, or fracking. The group says forcing water and chemicals deep into shale deposits to extract gas threatens drinking water and the environment.

The group's website implores: "Tell Governor Cuomo: Don't Frack New York."

"You spend money lobbying, you have to register," said David Grandeau, former executive director of the state lobbying commission and now an attorney representing lobbyists and clients. On Monday, after an AP article appeared on the group, he added: "It's clearly lobbying" and said the commission "missed the boat."

A good-government advocate said the lobbying regulator, the Joint Commission on Public Ethics, should look into the case.

"When someone is trying to influence or change public opinion, there's always a concern if the public doesn't know exactly how much money they are spending to do that," said Barbara Bartoletti, of the League of Women Voters. "I don't know if they are splitting hairs between educating the public or lobbying."

The commission cannot confirm or deny it will take on any case, spokesman John Milgrim said.

Ravi Batra, a former member of the commission board, called it an important issue.

"When celebrities get involved in influencing public opinion, it behooves everyone to make sure the law is followed to the letter," he said.

There's no public record of how much money Artists Against Fracking has spent, but its website contains links for visitors to make donations, which are directed to the Sustainable Markets Foundation. Although the foundation is an established charitable organization and its donations are recorded publicly, it isn't registered with New York as a lobbying client, either.

Under New York law, however, it appears Artists Against Fracking is required to be a registered lobbyist because the law hinges on spending over $5,000. The group hasn't filed lobbying reports, so the amount it has spent and what it was spent on isn't known publicly. Experts in Albany say the website and public events appear to have cost well over $5,000.

The widow and son of musician John Lennon recently attended an anti-fracking event in Albany with Ruffalo, actors Zooey Deschanel, Alec Baldwin and Hugh Jackman, and singer Lady Gaga, along with other longtime activists such as David Crosby and Paul McCartney.

A week ago, Artists Against Fracking widely released a music video done through Skype from various locations featuring dozens of entertainers singing a Sean Lennon song, "Don't Frack My Mother." In it, Ono sings part of the chorus, "Don't frack me!"

Failing to register as a lobbyist is not a criminal offense. Commonly, when a person new to lobbying is believed to have failed to lobby as required by law that person is given a chance to submit a lobbing form and pay a $200 fee.

One of the main players supporting fracking, the Independent Oil & Gas Association of New York, is registered.

Lobbying is big business in New York. The New York Public Interest Research Group reported that more than $220 million was spent lobbying in 2011 — and that was before the fracking debate really heated up.

The biggest penalty for failure to follow the lobbying law resulted in a $250,000 fine against Donald Trump and others over casinos in 2000, and the Philip Morris tobacco company was hit with a $75,000 fine in 1999.