Facebook has faced criticism from Republican and Democratic US lawmakers who demanded the social media company be more forthcoming about data it has shared with four Chinese firms.
The bipartisan criticism reflected rising frustration in Congress about how Facebook protects the privacy of the more than 2 billion people who use its services worldwide.
The leaders of the US House of Representatives Energy and Commerce Committee accused Facebook chief executive Mark Zuckerberg of failing to disclose the company's agreements with the Chinese firms when he appeared before them in April and testified about Facebook's sharing of users' personal information with third parties.
"Clearly, the company's partnerships with Chinese technology companies and others should have been disclosed before Congress and the American people," the panel's Republican chairman, Greg Walden, and top Democrat Frank Pallone said.
Facebook responded that Zuckerberg spent more than 10 hours responding to lawmakers' questions.
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"The arrangements in question had been highly visible for years - with many manufacturers advertising these features. But with fewer and fewer people relying on them, we proactively announced this spring we'd begin winding them down," the company said in a statement.
It has said the contracts with smartphone maker Huawei Technologies and other Chinese firms were standard industry practice and necessary to ensure that people who bought electronic devices had ready access to Facebook services.
Facebook said it had control over the data sharing all along and that other tech firms struck similar arrangements with US and Chinese companies in the early days of smartphones.
The company confirmed on Tuesday that Huawei, computer maker Lenovo and smartphone makers OPPO and TCL Corp were among about 60 companies worldwide that received access to some user data, after they signed contracts to re-create Facebook-like experiences for their users.
Huawei, the world's third-largest smartphone maker, has come under scrutiny from US intelligence agencies that have said that Chinese telecommunications companies provide an opportunity for foreign espionage and threaten critical US infrastructure.
Huawei said in a statement it had never collected or stored any Facebook user data.
Lawmakers expressed concern after The New York Times reported that the data of users' friends could have been accessed without their explicit consent. Facebook denied that, and said the data access was to allow its users to access account features on mobile devices.
In a separate letter, the Senate Commerce, Science and Transportation Committee pressed Facebook for more information, while the Senate Intelligence Committee's top Democrat urged Facebook to release further details.
Congressional aides have said Facebook has not answered hundreds of questions from lawmakers after Zuckerberg's April testimony before two committees.
Several aides said lawmakers were waiting for Facebook's answers before deciding on whether to hold additional hearings.
