A court in Pakistan has ordered the authorities temporarily to block the Facebook social networking site.
The order came when a petition was filed after the site held a competition featuring caricatures of the Prophet Muhammad.
The petition, filed by a lawyers' group called the Islamic Lawyers' Movement, said the contest was "blasphemous".
A message on the competition's information page said it was not "trying to slander the average Muslim".
"We simply want to show the extremists that threaten to harm people because of their Muhammad depictions that we're not afraid of them," a statement on the "Everybody Draw Mohammed Day" said.
"They can't take away our right to freedom of speech by trying to scare us into silence."
The information section of the page said that it was set up by a Seattle-based cartoonist, Molly Norris.
It contains caricatures of the Prophet Muhammad and characters from other religions, including Hinduism and Christianity, as well as comments both critical and supportive of Islam.
Publications of similar cartoons in Danish newspapers in 2005 sparked angry protests in Muslim countries - five people were killed in Pakistan.
Already the Pakistani press has reported protests against Facebook on Wednesday by journalists outside parliament in Islamabad, while various Islamic parties are also reported to be organising demonstrations.
Correspondents say that the internet is uncensored in Pakistan but the government monitors content by routing all traffic through a central exchange.
Justice Ejaz Ahmed Chaudhry of the Lahore High Court ordered the department of communications to block the website until 31 May, and to submit a written reply to the petition by that date.
An official told the court that parts of the website that were holding the competition had been blocked, reports the BBC Urdu service's Abdul Haq in Lahore.
But the petitioner said a partial blockade of a website was not possible and that the entire link had to be blocked.
The lawyers' group says Pakistan is an Islamic country and its laws do not allow activities that are "un-Islamic" or "blasphemous".
The judge also directed Pakistan's foreign ministry to raise the issue at international level.
In the past, Pakistan has often blocked access to pornographic sites and sites with anti-Islamic content.
It has deemed such material as offensive to the political and security establishment of the country, says the BBC's M Ilyas Khan in Islamabad.
In 2007, the government banned the YouTube site, allegedly to block material offensive to the government of Pervez Musharraf.
The action led to widespread disruption of access to the site for several hours. The ban was later lifted.