By Bob Sullivan UPDATED Jan. 16, 3:15 p.m. ET -- Opponents of controversial federal anti-piracy legislation known as SOPA seem to be picking up steam. Supporters of the legislation in both houses of Congress appear have backed off, the Obama administration has expressed concerns with the legislation, and an Internet blackout slated for Wednesday is picking up supporters.

A House subcommittee was slated to prepare the Stop Online Piracy Act, or SOPA, for a vote later this month; the Senate had planned a vote on the companion bill, PIPA (The Protect IP Act,) even sooner. Now, it appears both votes will be delayed.

SOPA opponents are rallying around an effort to call attention to the legislation by convincing Web sites to "go dark" on Jan. 18, and display only a simple message of protest on a black background. On Monday, Wikipedia co-founder Jimmy Wales announced that his website will go dark for 24 hours starting at midnight ET Tuesday, following the lead of other high-profile promised blackouts. Reddit.com will go black from 8 a.m.- 8 p.m. on Wednesday. The hacker group Anonymous also encouraged others to join in the 12-hour blackout, and garnered a lot of attention with its Twitter post using the hashtag #BlackoutSOPA.