The official Reddit Blog says they will blackout the service, in protest of SOPA (Stop Online Piracy Act) on January 18th from 8am – 8pm EST.
It makes sense as the bill would essentially force many sites, such as Reddit, to shut down.
Reddit members have rallied together to fight SOPA, and you can see their activities on their sub-reddit /r/sopa. Until now the protests coming out of Reddit have been by members. This marks the first official action taken by Reddit itself to protest the law.
Lets all hope he can convey the problems with SOPA, and convince the legislators not to pass it.