Encyclopedia giant Wikipedia, popular news-sharing site reddit, browser pioneer Mozilla, photo-sharing favorite Twitpic and even ICanHazCheezburger.com are blocking access to content throughout Wednesday, symbolizing what the bill may allow content creators to do to sites they accuse of copyright infringement. Other websites, including Google, are expressing solidarity with the protests by featuring anti-SOPA content on home pages.

The online protests are being joined by a physical demonstration in New York City, where thousands of representatives from the city’s tech industry plan to demonstrate outside the offices of Sens. Chuck Schumer (D-N.Y.) and Kristen Gillibrand (D-N.Y.), co-sponsors of the Senate version of SOPA, beginning at 12:30 p.m. As pressure has mounted, both have expressed willingness to compromise.

SOPA would give both the government and major corporations the power to shut down entire websites accused of copyright infringement with neither a trial nor a traditional court hearing. The legislation is aggressively backed by Hollywood movie studios and major record labels, along with several major news providers, including Fox News and NBC-Universal, which have largely shied away from coverage of the bill.

The burst of opposition to SOPA and its Senate companion, Protect IP (or PIPA, for short), has caught many lawmakers, who thought they were endorsing a fairly non-controversial anti-piracy bill with strong corporate support, off guard. Senate co-sponsors of the bill regrouped on Tuesday, huddling in the Capitol with major industry backers of the bill.

In December, HuffPost reported that Sen. Dianne Feinstein (D-Calif.), a Protect IP co-sponsor with deep ties to both Hollywood and the technology industry, thought disputes between two of her most prominent corporate constituencies had been worked out. After that story ran, Feinstein attempted to broker a compromise, calling both tech companies and film studios.

Walt Disney Co. President and CEO Bob Iger declined the invitation on behalf of content providers. “Hollywood did not feel that a meeting with Silicon Valley would be productive at this time,” said a spokesperson. The meeting took place with only tech companies present. Feinstein, once a reliable vote for the existing version of Protect IP, is now working hard to amend the bill, according to Senate Democratic aides.

But finding common ground is more difficult in this case than in most intra-corporate squabbles, because the two sides — or powerful elements within them, at least — have largely irreconcilable world views. One senior Senate aide said that the technology side consistently refuses to specify precise changes they want to the bill. Indeed, improving the bill would be counterproductive if the ultimate goal is killing it outright — which it certainly is for many elements of the anti-SOPA coalition.

“That’s a high-stakes risk,” said the senior aide, “because if they don’t have 41 votes, then what?”