Some of the web's biggest names have backed mass protests over internet surveillance carried out by the US National Security Agency (NSA).
The Restore the Fourth movement - referring to the US constitution's fourth amendment - said it wants to end "unconstitutional surveillance".
Reddit, Mozilla and Wordpress are among the big web names backing the action, due to take place on Thursday.
Almost 100 events have been planned across the US.
An interactive map detailing their locations has been published.
The site quotes a line from the fourth amendment which pledges "the right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures".
As well as the "real-world" protests, many influential websites plan to display messages of protest on their homepages on Thursday, co-ordinated by a group called the Internet Defence League (IDL).
The action has taken inspiration from similar efforts that took place last year.
Wikipedia, Google and others went "dark", or put black boxes over parts of their pages, to show their disagreement with proposed anti-piracy measures being discussed by US lawmakers.
In reaction to the revelations made by whistleblower Edward Snowden, Mozilla, maker of the widely used Firefox browser, launched stopwatching.us - a petition calling for full disclosure of the US's "spying" programmes.
At the time of writing, the site had amassed 536,559 signatures. Dissident Chinese artist Ai Weiwei is listed as being among the petition's backers.
The demand comes at a time when one top US intelligence official was forced to apologise for telling Congress in March that the NSA did not have a policy of gathering data on millions of Americans.
National intelligence director James Clapper said in a letter to the Senate intelligence committee that his answer had been "clearly erroneous".