By Supantha Mukherjee and Foo Yun Chee

STOCKHOLM/BRUSSELS (Reuters) - TikTok, Shein, Xiaomi (OTC:XIACF) and three other Chinese companies were named in a privacy complaint filed on Thursday by Austrian advocacy group Noyb which claimed the firms were unlawfully sending European Union user data to China.

Noyb is known for filing complaints against American companies such as Apple (NASDAQ:AAPL), Alphabet (NASDAQ:GOOGL) and Meta (NASDAQ:META), which has led to several investigations and billions of dollars in fines.

Vienna-based Noyb (None Of Your Business) said this is their first complaint against Chinese firms.

Noyb has filed six complaints in four European countries for suspension of data transfers to China and is seeking fines that can reach up to 4% of a firm's global revenue.

Noyb said Alibaba (NYSE:BABA)'s e-commerce site AliExpress, retailer Shein, TikTok and phone maker Xiaomi admit to sending Europeans’ personal data to China, while retailer Temu and Tencent's messenger app WeChat transfer data to undisclosed "third countries" likely China.

Under European Union's General Data Protection Regulation (GDPR) privacy regime, data transfers outside the EU are only allowed if the destination country doesn't undermine the protection of data.

"Given that China is an authoritarian surveillance state, it is crystal clear that China doesn't offer the same level of data protection as the EU," said Kleanthi Sardeli, a data protection lawyer at Noyb. "Transferring Europeans’ personal data is clearly unlawful – and must be terminated immediately.

Chinese companies, notably ByteDance-owned TikTok, have been facing off with regulators in various countries. TikTok is planning to shut its app for U.S. users from Sunday, when a federal ban on the social media app is due to come into effect.

The European Commission is also investigating TikTok over its suspected failure to limit election interference, notably in the Romanian presidential vote in November.