Big names from Silicon Valley went head-to-head with media giants at a House hearing Wednesday on the Stop Online Piracy Act (SOPA), which would punish companies for posting pirated content online.

Several lawmakers at the hearing said they supported the legislation, introduced last month by House Judiciary Committee Chairman Lamar Smith (R-Texas), which was originally aimed at shutting down foreign sites that posted intellectual property created by U.S. firms.

But critics say it goes too far.

Internet giants including Yahoo, Google, Facebook and the Consumer Electronics Association have joined forces to oppose the legislation, which they say would give the government too much power to shut down Web sites accused of pirating or counterfeiting content.

“Inexplicably, and almost overnight, SOPA has morphed into a full-on assault against lawful U.S. Internet companies,” said Markham C. Erickson, executive director of NetCoalition, a group representing Web firms and public interest groups opposed to the law.

Supporting the bill is a powerful group of lobbies interested in protecting intellectual property, including the Motion Picture Association of America, pharmaceutical makers, media firms and the U.S. Chamber of Commerce.

“Fundamentally, this is about jobs,” said Michael O’Leary, who represented the Motion Picture Association of America at a hearing Wednesday.

The Chamber estimates that Hollywood studios, record labels and publishing houses lose $135 billion in revenues each year from piracy and counterfeiting.

This clash of the Titans over SOPA has created major schisms.

Yahoo has already canceled its membership in the U.S. Chamber of Commerce over SOPA, and Google is threatening to walk too.

For more on the bill, Post Tech’s Hayley Tsukayama has helpfully gathered five things to know about SOPA for your reading pleasure.