The announcement came via a series of Tweets this afternoon by Jimmy Wales, and was immediately picked up by Techmeme and others.

SEE ALSO: Wikipedia Homepage Confirms Site Will Go Black For 24 Hours

The move comes as a surprise because it appeared that SOPA opponents had succeeded in halting the controversial legislation. On Friday afternoon, Republican sponsors said they were removing key provisions of the bill and, on the weekend, the White House issued a statement suggesting it was withdrawing support.

SOPA supporters say the bill is needed to curtail “rogue” foreign websites but critics say it goes too far by tampering with the architecture of the internet and imposing China-style censorship. The debate has been characterized by fevered rhetoric on both sides, including by news baron Rupert Murdoch who this weekend tweeted “So Obama has thrown in his lot with Silicon Valley paymasters who threaten all software creators with piracy, plain thievery.”

The Wikipedia announcement confirms the company is participating in the internet “black-out” that has been proposed for January 18th. Some began calling this the “nuclear option” following rumors that tech giants like Google (NSDQ: GOOG) and Facebook might participate.

If Wikipedia goes forward with the blackout, the SOPA debate is likely to expand beyond the tech and media sphere where it has percolated until now. Unlike other blackout proponents like Reddit which are largely the preserve of tech insiders, Wikipedia is read broadly by the general public. Wikipedia’s motives for going forward with the blackout are not entirely clear but it appears from Wales’ Twitter feed that he and others are worried the political halt is simply a tactical maneuver (see graphic below).

In other SOPA developments, influential tech publisher Tim O’Reilly explained his justifications for opposing the bill and the New York Times (NYSE: NYT) provided an analysis of the weekend’s political jostling.