(Add Senator Wyden quote, background)
WASHINGTON, Feb 27 (Reuters) - The U.S. House of Representatives on Tuesday overwhelmingly passed legislation to make it easier to penalize operators of websites that facilitate online sex trafficking, chipping away at a bedrock legal shield for the technology industry.
The bill's passage marks one of the most concrete actions in recent years from the U.S. Congress to tighten regulation of internet firms, which have drawn heavy scrutiny from lawmakers in both parties over the past year due to an array of concerns regarding the size and influence of their platforms.
The House passed the measure 388-25. It still needs to pass the U.S. Senate, where similar legislation has already gained substantial support, and then be signed by President Donald Trump before it can become law.
Speaker Paul Ryan, in a statement before the vote, said the bill would help "put an end to modern-day slavery here in the United States."
Several major internet companies, including Alphabet Inc's Google and Facebook Inc, had been reluctant to support any congressional effort to dent what is known as Section 230 of the Communications Decency Act, a decades-old law that protects them from liability for the activities of their users.
But facing political pressure, the internet industry slowly warmed to a proposal that gained traction in the Senate last year, and eventually endorsed it after it gained sizeable bipartisan support.
Republican Senator Rob Portman, a chief architect of the Senate proposal, said in a statement he supported the House's similar version and called on the Senate to quickly pass it.
The legislation is a result of years of law-enforcement lobbying for a crackdown on the online classified site backpage.com, which is used for sex advertising.
It would make it easier for states and sex-trafficking victims to sue social media networks, advertisers and others that fail to keep exploitative material off their platforms.
Some critics warned that the House measure would weaken Section 230 in a way that would only serve to further help established internet giants, who possess larger resources to police their content, and not adequately address the problem.
"This bill will only prop up the entrenched players who are rapidly losing the publics trust," Democratic Senator Ron Wyden, an original author of Section 230, said. "The failure to understand the technological side effects of this bill - specifically that it will become harder to expose sex-traffickers, while hamstringing innovation - will be something that this Congress will regret." (Reporting by Dustin Volz; editing by Sandra Maler and Lisa Shumaker)