Liberal, conservative and political groups in between have joined forces in a rarely documented event, gathering in mass opposition against plans by Internet service providers to charge mass e-mailers to send out messages.

Grassroots organizations are fired up over America Online's and Yahoo's decisions to place a fee on groups that send e-mail to large numbers of users without first being sorted through junk mail filters. Opponents say the new fees will limit their ability to reach their members on legislation, candidates and other issues of importance to them.

"Our biggest concern is that it's going to hamper our ability to get information to our members so that they are able to contact their congressman or senator," said William Greene, president of RightMarch.com, a conservative grassroots group with an estimated one million members nationwide.

Greene said most members have AOL and Yahoo e-mail addresses, to which RightMarch.com sends out about three million e-mail messages per week. The new fees are "going to put a real damper on their participation in the democratic process."

Yahoo has already clarified that it will apply its charges to transaction mail, which are bank account statements or purchase receipts. Political and nonprofit groups will not be charged to send e-mail to members that use Yahoo! Mail.

"Yahoo delivers millions of messages each day from non-profit groups and political organizations, and these groups can continue to send messages to Yahoo! Mail users in exactly the same way, at no cost," a Yahoo spokeswoman said.

AOL and Yahoo defended their decisions to charge for mass mailings by saying it is an effort to protect consumers by cracking down on spam and Internet scam artists. The fee service, to be provided through a company called Goodmail Systems, will ensure senders that their messages won't be filtered and will carry a seal that proves to subscribers that they are legitimate e-mails.

The service aims to add an additional layer of protection against e-mail identity theft scams and "phishing" attacks, and seeks to boost customers' security without charging a fee, Yahoo's spokeswoman said.

But up in arms over the decision are roughly 500 groups that have signed an open letter opposing the plan. The letter cites concerns that AOL is creating a two-tier system that will prevent smaller groups with low budgets from getting their messages out. Among the groups that have signed onto the letter are Democracy for America, MoveOn.org, Common Cause, Earthjustice, Gun Owners of America and the Democratic National Committee.

"They are invading the right that members have to decide what e-mails they want to receive," said Noreen Nielsen, a spokeswoman for Democracy for America, a liberal political action committee founded by Democratic National Committee Chairman Howard Dean.

Democracy for America was molded around Dean's success in building an Internet campaign fundraising database for his 2004 presidential bid and relies on the World Wide Web to deliver electronically campaign information on Democratic candidates. Nielsen called AOL's fees an e-mail tax, saying it will hurt grassroots organizations that can't afford to pay for it.

AOL has not been totally deaf to the outcry. It has responded to concerns by offering some qualifying groups a waiver to the fee. AOL's Enhanced White List is a free service for nonprofit organizations that meet the ISP's anti-spam and e-mail requirements. The Enhanced White List also allows nonprofits to use third-party e-mail accreditation to authenticate messages.

"We want to make sure that not-for-profits who depend on timely communication with their members get all of the privileges of this powerful medium," said Charles Stiles, AOL Postmaster, in a statement.

"There will be no requirement, ever, for not-for-profits who deliver e-mail to AOL members to pay for e-mail certification and delivery," Stiles said.

AOL did not respond to repeated calls for comment, but distributed a press release to answer questions about who could qualify for the free service. Groups that have tax-exempt status with the Internal Revenue Service are able to send mass e-mail for free, according to the press release.

But political groups like RightMarch.com and Democracy for America, which fall under a different IRS tax status, say they aren't sure they could qualify for the exemption. The group that helped put together the open letter adds that it worries this is the first step to a pay-to-send system that would charge for any e-mail ever sent.

"We realized that the big problem was that AOL was taking some of the money," said Danny O'Brien, a spokesman for the Electronic Frontier Foundation, a nonprofit digital rights advocacy group.

O'Brien said AOL's plan won't fight spam, and could even make things worse since spammers will find ways around the system to deliver e-mail for free.

"It's making people who aren't spammers pay," he said.