The US House of Representatives has approved a bill that forces anyone operating a public Wi-Fi connection to report illegal images sent or received over the service.

The Securing Adolescents From Exploitation-Online Act (Safe Act) is designed to catch users swapping or accessing images of child pornography.

Rather than simply affecting ISPs and other web-access businesses, the legislation includes Wi-Fi connections in areas such as libraries, hotels and coffee shops, as well as those operated by private individuals.

Any service failing to report illegal traffic faces a fine of up to $150,000 for a first offence, rising to a maximum of $300,000 for further offences.

Wi-Fi company Fon, which allows individuals to securely share Wi-Fi connections, suggested that its users may not be responsible for reporting illegal images.

"The side that's open is monitored by Fon so the company can see what's going on," a spokesman said.

The Safe Act was passed in the House of Representatives by 409 votes to two.

Law makers used a system designed to push legislation through quickly which meant that it did not receive a hearing, was not voted on in committee and was not put up for public review.

The Act requires 'electronic communication services' or 'remote computing services' to report any illegal information to CyberTipline run by the National Center for Missing and Exploited Children.

The Safe Act adds to existing legislation that requires ISPs to report anyone accessing child porn to the National Center for Missing and Exploited Children.