Markham Erickson of NetCoalition - a group consisting of the trio and other popular destinations such as PayPal, Yahoo and Amazon - confirmed that the drastic move was already "under consideration".
"Mozilla had a blackout day and Wikipedia has talked about something similar," the director told Fox News. "A number of companies have had discussions about that.
"This type of thing doesn't happen because companies typically don't want to put their users in that position. The difference is that these bills so fundamentally change the way the internet works. People need to understand the effect this special-interest legislation will have on those who use the internet."
He added that the move could be "just the tip of the iceberg in terms of response" from anti-SOPA organisations.
The SOPA bill has been backed by motion picture and recording industries who hope to permanently eliminate online theft, though there are concerns that its piracy restrictions could have a harmful effect on legitimate websites.
The bill has been backed by names as significant as Adidas, Burberry and News Corporation.
Facebook and Google first voiced their opposition to the act earlier this month.
Last week, Google was criticised by the International Federation of the Phonographic Industry (IFPI) for having failed to tackle illegal file-sharing and copyright piracy.