WASHINGTON (AP) -- The Supreme Court on Friday upheld a Texas law aimed at blocking children under 18 from seeing online pornography.

Nearly half all states have passed similar age verification laws as smartphones and other devices make it easier to access online porn, including hardcore obscene material.

The 6-3 ruling comes after an adult-entertainment industry trade group called the Free Speech Coalition challenged the Texas law. The court split along ideological lines.

The group said the law puts an unfair free-speech burden on adults by requiring them to submit personal information that could be vulnerable to hacking or tracking. It agreed, though, that children under 18 shouldn't be seeing porn.

A leading adult-content website, Pornhub, has stopped operating in several states, citing the technical and privacy hurdles in complying with the laws.

The Supreme Court has confronted the issue before. In 1996, it struck down parts of a law banning explicit material viewable by kids online. A divided court also ruled against a different federal law aimed at stopping kids from being exposed to porn in 2004 but said less restrictive measures like content filtering are constitutional.

Texas argues that technology has improved significantly in the last 20 years, allowing online platforms to easily check users' ages with a quick picture. Those requirements are more like ID checks at brick-and-mortar adult stores that were upheld by the Supreme Court in the 1960s, the state said.

District courts initially blocked laws in Indiana and Tennessee as well as Texas, but appeals courts reversed the decisions and let the laws take effect.

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Associated Press writer Jonathan Mattise in Nashville contributed to this report.

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