A US congressional panel has criticised internet firm Yahoo for not giving full details to a probe into the jailing of a reporter by Chinese authorities.
Yahoo's senior officers say the firm has to comply with local laws
Yahoo had been "at best inexcusably negligent" and at worst "deceptive" in evidence given to the House Foreign Affairs Committee last year, it said.
Yahoo's Michael Callahan originally told Congress he did not know why China wanted the reporter's details.
Shi Tao was jailed after Yahoo helped Chinese officials identify him.
Chief executive Jerry Yang said his firm had always been open with Congress and that it was "fully committed to protecting human rights".
Yahoo has previously said it had to comply with Chinese laws to operate in the country.
Democratic Representative Tom Lantos, chairman of the House committee, issued a stinging rebuke to the US-based internet giant at Tuesday's hearing.
At issue is whether Michael Callahan, Yahoo's executive vice-president and general counsel, gave false information to the panel during an investigation in February 2006.
Mr Callahan said then that he did not know why the Chinese authorities wanted to trace Shi Tao - who was jailed for 10 years - but it has since emerged that other Yahoo employees had a document stating it was to do with the "suspected illegal provision of state secrets".
Mr Callahan wrote a letter to Congress last week to apologise and stating that the pertinent information only came to his attention months after he gave testimony.
Mr Lantos said any big company operating in China should have been aware of the authorities' repression of free speech.
He also questioned how Mr Callahan could not have known of the document referring to "state secrets" - a charge commonly used to prosecute dissidents and pro-democracy activists.
Chinese computer users are barred from accessing some websites
"Yahoo claims that this is just one big misunderstanding," Mr Lantos said.
"Let me be clear - this was no misunderstanding. This was inexcusably negligent behaviour at best, and deliberately deceptive behaviour at worst."
Mr Callahan responded that there had been confusion over the information Yahoo had about the demand made by Chinese authorities.
He apologised for the "misunderstanding" and for not letting the House committee know when the additional information came to his attention.
Urged by Mr Lantos to "beg the forgiveness" of Shi Tao's mother, who was present at the hearing, both Mr Callahan and Mr Yang turned and nodded silently to her.
Mr Lantos added: "I do not believe America's brightest and best companies should be playing integral roles in China's notorious and brutal political repression apparatus."
Shi Tao was jailed for sending on to foreign websites an e-mail from the ruling Communist Party warning journalists not to cover the 15th anniversary of the Tiananmen Square massacre in 2004.
Last month, the House committee backed legislation which would prevent internet companies such as Yahoo from co-operating with authorities in China and elsewhere.
Under the legislation, companies would also have to reveal terms and phrases they filtered in certain countries.
The bill, introduced by Republican representative Chris Smith, still needs approval from the House Energy and Commerce Committee.
The Chinese government enforces strict laws on internet use, blocking content it considers a threat, including references to the Tiananmen Square massacre and notable dissidents.