A diverse coalition of groups, many of them nonprofits, launched on Tuesday a campaign to pressure America Online Inc. into halting plans for a pay-to-send email system.

The coalition of 50 groups announced in a teleconference with reporters included political action committee MoveOn.org, Gun Owners of America, the Electronic Frontier Foundation, the Association of Cancer Online Resources, the Humane Society, the AFL-CIO, and the media reform group Free Press. Among the individuals supporting the group was Craig Newmark, founder of popular classified ads site Craigslist.

In pressuring AOL, the coalition plans to circulate petitions among its memberships and to gather signatures online from the public in an open-letter to AOL that's available through the Web site DearAOL.com.

AOL, a division of Time Warner Inc., and Yahoo Inc. announced in January plans to offer a certified email system operated by Goodmail Systems Inc. Organizations that paid would be guaranteed that their bulk email would be delivered to the inboxes of the portals' email subscribers. The messages would arrive with an icon authenticating the sender, and email subscribers would have had to agree in advance to receive the email.

AOL planned to launch the service this quarter, and Yahoo expected to begin later in the year.

In denouncing pay-to-send systems Tuesday, the coalition argued that certified email is counter to the open system that has led to the wide adoption of email, which can be received and sent by anyone with a computer. Introducing a paid system, the group argued, would inevitably establish a two-tier system in which only people and organizations willing to pay Internet service providers could be certain their messages would be delivered.

"When there's a free service and a paid service, I can't think of any examples where the paid service isn't better," Eli Pariser, executive director of civic action for MoveOn.org, said.

The inevitable degradation of the free service, in the group's opinion, was just one of several problems. Paid email would also place nonprofits at a disadvantage, since many could not afford to pay; and therefore hamper the free flow of information on the Internet.

"The future of the Internet as we know it is at risk here when you allow corporations, such as AOL and others, to impose this sort of discriminatory regime over information and to profit from it in a way that serves no one but themselves," Timothy Karr, campaign director of Free Press, said. "The free information that Americans have come to expect from this very democratic communication tool has become compromised." The coalition also argued that a paid system would do nothing to reduce spam or to improve the technology used to separate the annoying, unsolicited messages from marketers, phishers and pornographers. On the contrary, AOL and other Internet service providers adopting certified-email systems would more likely shift their focus over time from spam filters to paid services.

AOL contends that nothing would change for people currently using free Web mail, arguing that it would lose subscribers to its many competitors if it failed to maintain a quality service.

For companies or marketers, however, the paid system would guarantee their email and all its contents, including attachments, would reach customers, or potential customers. Spam filters today often send legitimate mail to junk folders by mistake, or strip away links and attachments to battle against phishers and virus writers.

Collectively, the coalition could reach between 2 million and 4 million AOL subscribers just through their own memberships, Pariser said.

Nevertheless, AOL said it wouldn't be swayed by the coalition.

"We have the facts on our side, we have our members on our side and we have the credibility and recognition of doing the right thing for years, when it comes to safety and security and protecting the integrity of email on the Internet," AOL spokesman Nicholas Graham said. "We have stellar, totally pristine deliverability practices for email that will not change, and the plan, as it always has been, remains today.

"AOL will implement certified email in the next 30 days. Mark it on your calendar."

While most of the coalition did not plan to call for a boycott of AOL, Larry Pratt, executive director of Gun Owners of America, said his organization would, if AOL went ahead with its service.

"If AOL pulls the trigger on this plan, then that would be our response," Pratt said.

The coalition has chosen to go after AOL and not Yahoo, because the latter in meetings appeared more tentative about launching the service.

"We really felt that AOL had planted its flag in the ground much more clearly," Danny O'Brien, activism coordinator for the Electronic Frontier Foundation, said.

In addition, AOL was a large enough target that if the portal decided to nix the service, it would discourage other portals from trying something similar, O'Brien said.