Gaiman added his signature to an open letter to Congress along with other members of the creative community, including Trent Reznor, Aziz Ansari and OK Go.
"We fear that the broad new enforcement powers provided under SOPA and PIPA could be easily abused against legitimate services like those upon which we depend," the notice states.
"These bills would allow entire websites to be blocked without due process, causing collateral damage to the legitimate users of the same services - artists and creators like us who would be censored as a result,"
Ellis also voiced his opposition to the legislation, as has publisher Fantagraphics. X-Factor writer Peter David claims to be against the bill in its present form, but hit out at online piracy.
Posting on his blog, David criticised those who "endorsed the piracy, supported the piracy, enabled the piracy, felt their own actions weren't piracy, and now refuse to accept the consequences of their own actions".
Wikipedia, the world's sixth most popular website, went 'dark' for 24 hours this week in protest at SOPA and PIPA.
Barack Obama's US government said at the weekend that SOPA would not be passed in its current form, but the controversial legislation is not considered dead, while the broadly similar PIPA will go before the full US Senate next week.