Wikipedia and Reddit will shut down for 24 hours as a protest against congressional consideration of the Online Piracy Act.
"Student warning! Do your homework early. Wikipedia protesting bad law on Wednesday," Wales wrote in a Tweet.
The protest will apply only to the English version of the popular online encyclopedia and will last for 24 hours.
Wales estimated that the English Wikipedia receives about 25 million visits per day, but he said the site could receive even more visits during the blackout due to the publicity.
Wikipedia is the sixth most-visited website in the world, according to Web information company Alexa.
Visitors to the site on Wednesday will see a message opposing the House's Stop Online Piracy Act and the Senate's Protect IP Act. Wikipedia's users were still debating as of Monday afternoon which message to use.
"I hope Wikipedia will melt phone systems in Washington on Wednesday," Wales wrote.
Piracy is a huge problem but this is definitely not the way to deal with it.
The measures are designed to go after foreign websites that offer illegal copies of music, movies and TV shows with impunity. The legislation would empower the Justice Department and copyright holders to demand that search engines delete links to sites "dedicated" to copyright infringement. Ad networks and payment processors would be prohibited from doing business with the sites.
Movie studios, record labels and business groups say the measures are necessary to crack down on online copyright infringement, which is hurting businesses and destroying jobs.
But major Web companies say the bills would require them to police user-generated content. They argue the bills would stifle innovation and censor free speech.
The House has decided not to take up the bill while Harry Reid and the Democratic senate are going ahead with debate this week and plans to bring it to a vote on January24.