BEIJING— Chinese artist Ai Weiwei has called for an Internet boycott on July 1 — the anniversary of the Chinese Communist Party's founding — to protest a government plan requiring all computers produced in China to contain software that blocks access to pornographic and other sites considered  “unhealthy” for young people.

Using Twitter, Ai has posted a message asking his fellow citizens to "stop any online activities, including working, reading, chatting, blogging, gaming and mailing. Don't explain your behaviour.” The government's plan goes into effect July 1 and targets computers made in China for domestic sale. Critics worry that the censorship filter, called Green Dam, signals the beginning of a crackdown on groups and Web sites that the government fears or disapproves of. There have also been complaints that the government awarded the 41.7 million yuan ($6 million) contract to Jinhui Computer System Engineering without a transparent bidding process, which has made the company the country's most profitable software manufacturer.

Read more at the London Times.