Ai Weiwei, Edward Snowden, and Pussy Riot have partnered with AdBlock and Amnesty International on an online campaign to protest censorship. The campaign will launch at 4PM ET today and will only be visible to AdBlock users, with messages from the activists displayed where advertisements would normally be placed.

The global campaign will run throughout the day on March 12th, which is the World Day against Cyber Censorship. It also comes amid heightened concerns over government surveillance, which have been magnified during Apple's ongoing standoff with the FBI over encryption and national security. Amnesty International, a London-based rights group, has joined other privacy advocates in supporting Apple, arguing that allowing the government backdoor access to encrypted communications would threaten free speech and security.

In a press release, Amnesty said that clicking on the banners will direct users to content from people whose governments have sought to repress their speech. Messages from North Korean victims of online censorship will also be displayed alongside those from Snowden, Ai, and Pussy Riot. Earlier this week, Amnesty published a report detailing the extent to which North Korean leader Kim Jong-un has intensified the government's censorship regime since coming into power in 2011.

The messages from Snowden, Ai, and Pussy Riot — who are among the most well-known anti-censorship activists — are both ominous and urgent. "Even if you’re not doing anything wrong, you’re being watched and recorded," Snowden says in one spot. "Without freedom of speech there is no modern world, just a barbaric one," says Ai, a prominent Chinese artist and activist. "Authorities don’t just use handcuffs and arrests, but also media attacks," adds Pussy Riot, a Russian punk rock group whose members have been targeted by the government of President Vladimir Putin.

AdBlock's 50 million users may be surprised to see banners across the websites they visit on Saturday, but the company says it decided to make an exception in the name of an important cause.

"We’re showing you Amnesty International banners, just for today, because we believe users should be part of the conversation about online privacy," AdBlock CEO Gabriel Cubbage said in a statement. "Tomorrow, those spaces will be vacant again. But take a moment to consider that in an increasingly information-driven world, when your right to digital privacy is threatened, so is your right to free expression."