Senator Mark Warner, a Democrat who is vice chairman of the Senate Intelligence Committee, said he had written to the companies on Thursday and made the letters public.

Facebook said on Tuesday that it had data sharing partnerships with at least four Chinese companies including mobile device manufacturer Huawei Technologies Co Ltd [HWT.UL], the world’s third largest smartphone maker, which has come under scrutiny from U.S. intelligence agencies.

People holding mobile phones are silhouetted against a backdrop projected with the Twitter logo in this illustration picture taken in Warsaw September 27, 2013. REUTERS/Kacper Pempel/File Photo

Alphabet had previously announced strategic partnerships with Huawei and mobile device maker Xiaomi, as well as with Chinese technology platform Tencent.

Warner said in a statement that since 2012 “the relationship between the Chinese Communist Party and equipment makers like Huawei and ZTE Corp has been an area of national security concern.” ZTE is China’s No. 2 telecommunications equipment maker.

Warner asked Alphabet Chief Executive Larry Page if it had “third party partnerships” with ZTE, Lenovo or TCL and if it conducted audits to ensure that the companies were properly handling consumer data. He asked Twitter Chief Executive Jack Dorsey if the company had relationships with Huawei as well. Huawei is the world’s third-largest smartphone maker.

Google said in an emailed statement on Thursday, “We have agreements with dozens of (manufacturers) around the world, including Huawei. We do not provide special access to Google user data as part of these agreements, and our agreements include privacy and security protections for user data.”

Twitter declined to comment.The New York Times reported on Sunday that Facebook data of users’ friends could have been accessed without their explicit consent. Facebook denied that and said data access was to allow its users to access account features on mobile devices.

The revelation drew a firestorm of criticism from members of Congress, including some who said Facebook Chief Executive Mark Zuckerberg should have disclosed that information in testimony to Congress in April.

Facebook said that Huawei, computer maker Lenovo Group and smartphone makers OPPO and TCL Corp were among about 60 companies worldwide that received access to some user data after they signed contracts.