Paul Graham has put the kibosh on SOPA-supporting companies showing up at Y Combinator events, including the popular and investment-driven Demo Days.

Graham founded Y Combinator, an incubator and accelerator program that attracts some of the brightest minds and most interesting startups around the world. A Graham-imposed ban means the exiled parties might not have the best chance get in on early investment rounds — or acquisition deals when companies (and founders) are young enough to sell for a song.

SOPA, or the Stop Online Piracy Act, is a wildly unpopular (in Silicon Valley, at least) piece of legislation currently being bandied around on Capitol Hill. While the bill is intended to stop things like the sale of counterfeit goods and the piracy of music and movies, it also has some far-reaching and detrimental consequences for the entire Internet.

“In general terms, I dislike SOPA because it’s an instance of old,declining industries trying to restrain technical progress that threatens their obsolete business models,” Graham said in an email to VentureBeat.

“Specifically what I dislike about it is (a) the lack of due process and (b) the provisions that will require ISPs to censor the Internet for their users. Both of these seem deeply un-American.”

If SOPA and its sister bill, PIPA (Protect IP Act) are passed into law, sites like Scribd and Wikipedia, which have both taken a stand against the bill, could be crippled or even taken offline and deindexed from search engines completely.

When the full list of SOPA-supporting companies was published earlier today, Graham participated in the resulting discussion on Hacker News, the news discussion side of Y Combinator, saying, “Several of those companies send people to Demo Day, and when I saw the list I thought, ‘We should stop inviting them.’ So yes, we’ll remove anyone from those companies from the Demo Day invite list.”

Scribd and Wikipedia are each planning to use some creative self-censorship to raise awareness and encourage action against the bills. Also, a long list of Internet progenitors has published an open letter to Congress stating their reasons for opposing the bill.

“It’s hard to predict who will win in this fight, but it’s encouraging that Congress has decided to spend more time thinking about it,” Graham continued in his correspondence with VentureBeat.

“I think Congress means well. When SOPA’s supporters first presented the bill, it probably sounded to a lot of representatives like it was a good way to solve an important problem. But now they’ve seen that practically everyone who understands the Internet is strongly against the bill, I think they’ve started to ask questions about it.”

To contact the congressional representatives responsible for SOPA, check out the resources available at AmericanCensorship.org.