The 30 Days of Night creator has published a series of tweets opposing the controversial law, which allows service providers to suspend websites suspected of copyright infringements.
"SOPA does more than go after so-called 'piracy' websites," said Niles.
"SOPA takes away all due process, shuts down any site it deems to be against the law without trial, without notification, without due process...
"Nobody seems to give a s**t, or either they're scared. Either way, very disappointing. I guess when it affects them they'll get mad...
"I know folks are scared to speak out because a lot of us work for these companies, but we have to fight. Too much is at stake."
The US House Of Representatives this week released a list of organisations that support the anti-piracy bill, which includes Marvel Comics, its parent company Disney and DC Entertainment owners Time Warner.
Google, Facebook and Twitter are opposing the act, and are threatening a coordinated blackout if it is passed.
Wikipedia founder Jimmy Wales has said that he will blank out all of the online encyclopaedia's US pages if SOPA is made law.
A final decision on the act is expected when after the US Congress returns following its winter recess.