Many schools have already banned social network sites

The Deleting Online Predators Act tries to limit the access paedophiles have to the networking sites which have become hugely popular with minors.

The act has already been approved by a large majority in the House of Representatives.

Critics say the act is too broad and could mean a huge number of websites are cut off from users.

Net ban

The DOPA Act was introduced into the US legislative system by Congressman Michael Fitzpatrick. It passed 410 votes to 15 in a vote on 26 July.

Speaking before the vote was taken, he said: "The social networking sites have become, in a sense, a happy hunting ground for child predators."

The act covers federal institutions that received funding for computers and net access via the US E-Rate scheme - primarily schools and libraries. The American Library Association (ALA) estimates that two-thirds of US libraries receive this funding.

It requires these organisations to put in place filters to stop children viewing social networking sites where they might be subject to "unlawful sexual advances".

Critics fear many popular sites could be caught by the law

Social networking sites such as MySpace, Bebo, Facebook, Friendster and many others count large numbers of children among their users.

In both the UK and US many schools have already banned pupils from using these networks over fears that the children are taking risks with the amount of information they are posting.

The DOPA Act leaves the final definition of what counts as a social networking site to the Federal Communications Commission.

Critics say the act's broad description of what the FCC should take into account in its definition could mean a huge number of sites will be blocked by libraries.

The act says the FCC should consider any site that allows users to create and modify a profile, chat to other users and post personal information.

Those criticising the Act said this could mean that a huge number of websites, such as Slashdot, Amazon, blogging sites, wikis and news organisations could be cut off.

"DOPA is redundant and unnecessary legislation," said Leslie Burger, president of the ALA in a statement. She pointed out that the Children's Internet Protection Act already requires libraries to block net content that is harmful to children.

Some MySpace users have created an online petition to gather support for protests about the act. The petition, called Save your Space, aims to gather more than one million signatures in a month.

The act now passes to the Senate and a vote on its approval is likely to take place in early August.