UPDATE 2-Tech chief executives to defend key law in front of U.S. Senate panel on Wednesday

(Adds details from testimony, background)

By David Shepardson and Nandita Bose

WASHINGTON, Oct 27 (Reuters) - The chief executives of Twitter Inc, Facebook and Alphabet Inc will tell U.S. lawmakers at a hearing on Wednesday that a federal law protecting internet companies is crucial to free expression on the internet, according to written testimonies from the companies seen by Reuters.

Section 230, a provision of the 1996 Communications Decency Act, shields technology companies from liability for user-generated content and allows them to remove lawful but objectionable posts. It has come under heavy criticism from President Donald Trump and both Democratic and Republican lawmakers who have been concerned about Big Tech's content-moderation decisions.

Twitter Chief Executive Jack Dorsey will tell the Senate Commerce Committee on Wednesday that eroding the foundation of Section 230 "could collapse how we communicate on the Internet, leaving only a small number of giant and well-funded technology companies."

Facebook's Mark Zuckerberg warned that tech companies were likely to censor more to avoid legal risks if Section 230 is repealed. "Without Section 230, platforms could potentially be held liable for everything people say," he said.

Zuckerberg also said without the law, tech companies could face liability for doing even basic moderation, such as removing hate speech and harassment.

Alphabet-owned Google's Sundar Pichai said the company approached its work without political bias and was able to offer the information it does because of existing legal frameworks such as Section 230.

In addition to discussions on reforming the law, the hearing will bring up issues about consumer privacy and media consolidation.

On Tuesday, Senator Maria Cantwell, the top Democrat on the senate commerce panel, released a report on how big tech platforms have decimated the local news industry, including newspapers and broadcasters.

(Reporting by David Shepardson and Nandita Bose; Editing by Bernadette Baum)