A House legislative proposal has drawn fresh attention from Internet firms and venture capital investors who are at odds with Hollywood and record labels advocating for stronger laws.

Silicon Valley giants Twitter, Yahoo and LinkedIn also signed onto the letter that asks leaders of the Senate and House Judiciary Committees to be more specific in any new rules to ensure online firms aren’t liable for pirated material that may appear on their sites. A similar bill by Sen. Patrick Leahy (D-Vt.) passed the Senate in September.

Online giants say they support efforts to fight against illegal exchange of copyrighted material on the Internet. But they said in their letter the House Stop Online Piracy Act proposal would “expose law-abiding U.S. Internet and technology companies to new uncertain liabilities, private rights of action, and technology mandates that would require monitoring web sites.”

Specifically, they say language is too vague in the House bill and that it could make online sites like theirs responsible for pirated content. They say a safe harbor of the Digital Millennium Copyright Act of 1998 protects them from legal action as long as they show good faith to remove infringing content from their site.

Facebook CEO Mark Zuckerberg speaks during a news conference at Facebook headquarters in Palo Alto, Calif., in this May 2010 file photo. (ROBERT GALBRAITH/REUTERS)

Hollywood’s trade group, the Motion Picture Association of America, and the U.S. Chamber of Commerce have lobbied strongly in favor of the legislation, saying U.S. businesses are losing out on billions of dollars in revenues from the illegal distribution of movies, music and software.

“Copyright owners have long had the legal right to sue online copyright infringers, but as a practical matter enforcing rights online has often resembled a game of whack-a-mole, with new infringing sites always popping up,” says Stefan Mentzer, a partner in the Intellectual Property Practice at White & Case LLP.

Even though the House SOPA bill is aimed at shutting down foreign “rogue” sites that allow for piracy, the bill, the online firms say, could expose them to litigation and potentially lead enforcement officials to shut down their services.

Ahead of the Wednesday hearing, 10 House lawmakers, led by Rep. Anna Eshoo (D-Calif.), wrote Judiciary Committee Chairman Lamar Smith (R-Texas), author of SOPA, and ranking member John Conyers (D-Mich.) to protest the legislation.

Eshoo is the ranking member of the Communications and Technology Subcommittee and represents Silicon Valley businesses that are in her district.