Global hacking movement Anonymous has called for protesters to take to the streets in 16 cities around India on Saturday over what it considers growing government censorship of the Internet.

The call for demonstrations by the Indian arm of the group follows a March 29 court order issued in the southern city of Chennai demanding 15 Indian Internet providers block access to file-sharing websites such as Pirate Bay.

The order has resulted in access being denied to a host of websites that carry pirated films and music among other legal content, including www.isohunt.com and www.pastebin.com.

On Wednesday, the Anonymous forum fired an opening shot by attacking the website of state-run telecom provider MTNL, pasting the logo of the group -- the mask of 17th century revolutionary Guy Fawkes -- on www.mtnl.net.in.

In an open letter the same day, the group accused the government of trying to create a "Great Indian Firewall" to establish control on the web and issuing a "declaration of war from yourself... to us."

Internet users and supporters have been asked to join peaceful rallies in cities including the capital New Delhi and the tech hub of Bangalore, with detailed instructions issued online to participants.

Tech website www.pluggd.in reported the demonstrators have been asked to wear Guy Fawkes' masks, download a recorded message to play to police, and are to chant "United as one! Divided as zero! We are Anonymous! We are legion!"

Concerns about Internet freedom in India go beyond the court order in Chennai, however, and stem from an update to India's Information Technology Act that was given by the IT and communications ministry in April last year.

The new rules regulating Internet companies -- providers, websites and search engines -- instruct them that they must remove "disparaging" or "blasphemous" content within 36 hours if they receive a complaint by an "affected person".

Groups such as the Center for Internet and Society, a Bangalore-based research and advocacy group, have waged a year-long campaign for amendments to the rules, which were quietly released in April.

Industry groups have also objected, saying they are unclear on the changes which are in any case impossible to implement when it comes to acting on individual complaints about specific content.

"A lot of education is required in this field," secretary of the Internet Service Providers Association of India S.P. Jairath told AFP.

The government has also become embroiled in a row with social networks after Telecoms Minister Kapil Sibal held a series of meetings with IT giants Google, Yahoo! and Facebook last year to discuss the pre-screening of content.

The minister was said to have shown Internet executives examples of obscene images found online that risked offending Muslims or defamed politicians, including his boss, the head of the ruling Congress party, Sonia Gandhi.

Since these meetings, 19 Internet firms including Google, Yahoo! and Facebook have been targeted in criminal and civil cases lodged in lower courts, holding them responsible for content posted by users of their platforms.

Anonymous is a secretive "hacker-activist" network and is thought to be a loosely knit collective with no clearly defined leadership structure.

It has claimed dozens of online attacks on sites ranging from the Vatican to Los Angeles Police Canine Association, but is increasingly the target of law enforcement agencies who have arrested dozens of members.