A group of more than 20,000 supporters of US Democratic presidential candidate Barack Obama have used his official social network to organize an online protest against his stance on legislation set to be taken up by the US Senate.

The users of the social network MyBarackObama.com have organized a grassroots protest online that opposes Obama's support of the US Foreign Intelligence Surveillance Amendments Act (FISA). The act would continue the controversial surveillance of e-mail and phone calls by the US National Security Agency started after September 11 and would likely end lawsuits against the telecommunications carriers that participated in the program. The US House of Representatives voted to approve the legislation last month.

Jeff Jarvis, a blogger and associate professor and director of the interactive journalism program at the City University of New York, noted in a blog post that the protest could mark an important moment in "participatory, self-organized online politics," especially since Obama's campaign has built itself on the support of various grassroots efforts.

"When it's a grassroots organization that makes you - rather than a party - and you say you're beholden to them not to special interests and big money and lobbyists, well, then you really are beholden to them," he noted. "If they rise up from within to tell you that they don't like what you're doing -- when they use your own organizational tools to do that -- then I'd say you ignore them at your peril. Live by the crowd, die by the crowd."

Jarvis added that it will be interesting to see what type of power these self-organized groups wield if Obama ascends to the White House.

"Will his supporters at MyBarackObama continue to use these tools to influence him and government? And will he have to listen because he is beholden to them?" he asked.

Obama's campaign did not respond today to a request for comment on the online protest. However, the senator noted in a blog post last week that the ability to monitor individuals who want to attack the US is a "vital counter-terrorism tool" and that he believes it is necessary to keep the American people safe.

"The truth is that your organizing, your activism and your passion is an important reason why this bill is better than previous versions," Obama wrote. "No tool has been more important in focusing peoples' attention on the abuses of executive power in this Administration than the active and sustained engagement of American citizens."

Obama went on to note that, "When citizens join their voices together, they can hold their leaders accountable. I'm not exempt from that ... I cannot promise to agree with you on every issue. But I do promise to listen to your concerns, take them seriously, and seek to earn your ongoing support to change the country."