New mobile phone buyers in China must register their personal data under a new rule that many see as an invasion of privacy.
As of Wednesday, customers buying numbers for mobile phones must show their identity cards and foreigners must produce passports. The Ministry of Industry and Information Technology says the measure is aimed at curbing spam and telecommunication fraud.
But critics say they think the government is trying to increase its control over new communications technologies.
The official Xinhua news agency says services will not be affected for those who already have pre-paid SIM cards in their mobile phones.
Xinhua says China has more than 800 million mobile phone users compared to 300 million fixed-line users. Leading operators China Mobile, China Unicom and China Telecom all say they will implement the new rules.
Some information for this report was provided by AP and Reuters.