Message board website Reddit on Friday filed a lawsuit in Australia's highest court seeking to overturn the country's social media ban for children, calling it an intrusion on free political discourse and setting the stage for a protracted legal battle.

The San Francisco-based firm, which ranks Australia among its biggest markets, said in a High Court filing that the ban should be declared invalid because it interfered with free political communication implied by the country's constitution.

Even if the court upheld the ban, Reddit should be exempt since it did not meet the definition of social media, added the filing, which named the Commonwealth of Australia and Communications Minister Anika Wells as defendants.

The lawsuit, two days into the rollout of the world-first nationwide ban on people under 16 accessing social media, is the second such challenge after two teenagers representing an Australian libertarian group filed suit last month.

But the action from a Silicon Valley major with a $44 billion market capitalisation dramatically increases the resources available to continue a drawn-out court battle. Success for Reddit could open the door for other platforms to mount similar challenges.

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A spokesperson for Wells said the Australian government was "on the side of Australian parents and kids, not platforms" and would "stand firm to protect young Australians from experiencing harm on social media".

Health Minister Mark Butler said Reddit filed the lawsuit to protect profits, not young people's right to political expression, and "we will fight this action every step of the way".

"It is action we saw time and time again by Big Tobacco against tobacco control and we are seeing it now by some social media or big tech giants," he told reporters in Brisbane.

'Privacy and political expression'

Australia went live with the world's first legally enforced age minimum to access social media on December 10. Reddit and nine other platforms, including Meta's Instagram, Alphabet's YouTube and TikTok campaigned against the measure for more than a year before ultimately saying they would comply.

The platforms are required to bar underage users or face a fine of up to A$49.5 million ($33 million), while underage users and their caregivers do not face punishment. Platforms say they are using measures like age inference, based on a person's online activity, and age estimation, based on a selfie, to follow the rule.

Also Read: Australia's social media ban for children takes effect in world first

But the law "carries some serious privacy and political expression issues for everyone on the internet," Reddit said in a statement published alongside its court filing. "So, we are filing an application to have the law reviewed."

In the 12-page filing, the company said barring under-16s would impede political discourse.

"Australian citizens under the age of 16 will, within years if not months, become electors. The choices to be made by those citizens will be informed by political communication in which they engage prior to the age of 18," it said.