FILE PHOTO: Reddit app is seen on a smartphone in this illustration taken, July 13, 2021. REUTERS/Dado Ruvic/Illustration/File Photo

SYDNEY, Dec 12 (Reuters) - Message board website Reddit on Friday filed a lawsuit asking the High Court to overturn Australia's social media ban for people under 16 as well as its inclusion in it, calling the law an infringement of free political expression.

The U.S.-listed firm, which has operations in Australia, called the ban "invalid on the ground that it infringes the implied freedom of political communication," in a court filing signed by its lawyers, Perry Herzfeld and Jackson Wherrett.

The filing named the Commonwealth of Australia and Communications Minister Anika Wells as defendants. A spokesperson for Wells was not immediately available for comment, although the Australian government has said it is ready to fight any legal challenges to the law.

Two days earlier, Australia went live with the world's first legally enforced age minimum to access social media. 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 ($32.98 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.

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."

The lawsuit makes a second High Court challenge to the ban. Last month, two teenagers backed by an Australian libertarian state lawmaker filed a challenge which has a hearing in February.

Reddit has no plans to join other parties challenging the ban, a person familiar with the situation said.

($1 = 1.5011 Australian dollars)

(Reporting by Renju Jose and Byron Kaye in Sydney; Editing by Matthew Lewis)