WASHINGTON — Internet giants like Google, Facebook, YouTube and Twitter owe much of their success to a legal shield erected by Congress in 1996.

Known as Section 230, it has been called the rule that launched Big Tech. Though it drew little attention at the time, the law is now seen as a pillar of the wide-open global internet we know today.

While newspapers and TV stations can be held liable for any false and malicious content they publish or broadcast, internet platforms are treated differently under Section 230.

Congress passed the special free-speech rule to protect the new world of online communication. It said: “No provider or user of an interactive computer service shall be treated as the publisher or speaker of any information provided by another information content provider.”

Law professor and author Jeff Kosseff called Section 230 “the 26 words that created the internet” because it allowed websites to develop freely as platforms for the words, photos and videos of others.

And it went unchallenged in the Supreme Court — until now.

This week, the justices will hear two cases that may finally pierce that legal shield and dramatically alter the rules of the game for the internet.

And they are expected to consider a third case later this year involving the First Amendment rights of internet companies amid state efforts to regulate them.

The case to be heard on Tuesday began with a California family’s suit against Google and YouTube for allegedly aiding and abetting an act of international terrorism. Their daughter Nohemi Gonzalez was killed in Paris in November 2015 when Islamic State terrorists fired into a restaurant where the 23-year-old student was dining with two friends. It was part of an ISIS rampage in the city that killed 129 people.

Their lawsuit alleged that Google, which owns YouTube, had “knowingly permitted ISIS to post hundreds of radicalizing videos inciting violence and recruiting potential supporters to join the ISIS forces.” Further, they alleged that YouTube “affirmatively recommended ISIS videos to users.”

At issue on Tuesday is only their second claim. Can YouTube be sued over the algorithms it created to direct users to similar content — in this case allegedly directing potential terrorists to other ISIS videos? Or does Section 230 protect them against such claims?

More than four dozen tech firms, internet scholars and free-speech advocates have filed friend-of-the-court briefs arguing that the internet companies should not be held liable for using computer programs that direct users to content they might find interesting.

“Recommendation algorithms are what make it possible to find the needles in humanity’s largest haystack,” said Washington attorney Lisa S. Blatt, representing Google and YouTube. She warned that opening the door to lawsuits over algorithms “risks upending the modern internet.”

A federal judge had dismissed the family’s suit based on Section 230, and a divided 9th Circuit Court of Appeals affirmed that decision in 2021.

Until this term, the Supreme Court had refused to hear appeals involving the law. On several occasions, however, Justice Clarence Thomas called for “paring back the sweeping immunity courts have read into Section 230,” particularly in cases where websites knew they were posting dangerous lies or criminal schemes.

Some prominent liberals, including Judges Marsha Berzon and Ronald Gould on the 9th Circuit Court, have also called for paring back the scope of Section 230.

They have been joined by advocates — both liberal and conservative — who portray the internet as a cesspool of disinformation and hate speech, a home for stalkers and fraudsters and a contributor to teen suicides and mass shootings. Critics also say social media companies get rich and keep viewers online by amplifying the most extreme claims and the angriest voices.

Google and other tech firms were surprised in October when the high court voted for the first time to hear a direct challenge to Section 230 and decide whether websites like YouTube can be sued for their use of algorithms and targeted recommendations.

Their alarm grew in December when the Biden administration took the side of the plaintiffs in Gonzalez vs. Google and said YouTube could be sued for algorithms that “recommend” more videos to viewers.