Human-rights groups have condemned technology giants Google, Microsoft, Cisco and Yahoo for collaborating with China to censor the internet.

The four companies have been accused of putting profits before principles in their push to win market share in China.

In a briefing by the US Congressional Human Rights Caucus, the companies were condemned for allowing profits to precede democratic values such as freedom of speech.

All four companies have been summoned to a 15 February hearing by the House International Relations Subcommittee, which oversees human rights issues.

The briefing on Wednesday was led by Tim Ryan, who said the censorship involved preventing Chinese citizens from seeing websites not supported by the government. Both Google and Microsoft have admitted to engaging in censorship.

Yahoo has allegedly provided online information to China's government that led to a Chinese journalist going to jail.

There are also claims that Cisco has assisted the government in tracking down cyber-dissidents.

All four companies refused to participate in the briefing but Microsoft and Yahoo did release a joint statement calling on the US government to help solve censorship problems in China.

"We urge the United States government to take a leadership role in this regard and have initiated a dialogue with relevant US officials to encourage such government-to-government engagement," the statement said.

Anti-censorship groups Reporters Without Borders, Amnesty International and Human Rights Watch want Congress to introduce a uniform code of conduct to protect freedom of speech.

This story first appeared on Macworld.co.uk.