Australia's world-first teen social media ban was a ​modest, non-partisan and justified curb on political expression, a lawyer for the government told the top court ⁠on Wednesday, rejecting a legal ⁠challenge by Reddit.

Nearly a year since Australia banned large social media platforms from allowing under-16s to hold accounts, messaging platform ​Reddit and a libertarian advocacy group have sought ​to invalidate ⁠the law on grounds that it violates constitutionally protected speech.

The government is defending the law, calling it a necessary harm minimization measure.

A win for the plaintiffs would be a major setback not just for Australia but for lawmakers around the world who followed with similar measures in what has become a global movement to protect child physical and mental health in the digital age.

After a lawyer for Reddit told the court the law's imposition on free speech ⁠for ⁠minors was disproportionate to the benefits of keeping them off social media, Stephen Lloyd, for the government, said the ban was a relatively minor measure with proven positive effects.

"The burden is indirect and modest in extent," Lloyd told the court's seven-judge panel on the second day of hearings.

The law "incrementally" reduced children's ability to send and receive content online, while they could still view some content without ⁠an account, he added, noting it was "viewpoint neutral" so did not target any particular type of political expression.

Under the law, children and caregivers face no punishment but ​platforms can be fined up to A$99 million ($68.97 million) for systemic noncompliance.

So ​far, multiple studies including by Australian regulator the eSafety Commissioner have found that most of the country's under-16s still use social ⁠media, ‌and the ‌government has said it is preparing an enforcement ⁠lawsuit.

On Wednesday, Lloyd said it was ‌unclear if noncompliance was the result of weaknesses in age assurance technology or platforms' failure ​to implement it, but ⁠added that the law would contribute to the government's ⁠child protection aims regardless.

The hearing has been adjourned to a ⁠date to be ​decided, when the judges are expected to give a ruling.