SYDNEY, July 29 (Reuters) - Elon Musk's X accused Australia of trying to give its internet regulator unfair information-gathering powers and undermining U.S. law with plans for tougher enforcement of a teen social media ban.

Australia's world-first law barring accounts for under-16s took effect last December, drawing criticism from social media companies, mostly based in the United States.

But the contention by X, whose parent company is Musk's just-listed SpaceX, amounts to one of the world's most powerful people injecting a geopolitical element into the debate.

The plans did not give "due regard to procedural fairness, privacy, the broader impacts on online services, and Australia's digital economy", X told an Australian senate committee.

In its submission published on Tuesday, X took aim at plans to give the eSafety Commissioner wider rights of document discovery and double a maximum fine to A$99 million ($69 million).

The changes would "compel any person outside Australia ... to provide information and documents merely because they are 'affiliated' with a company," X said, a move it described as being "in clear conflict" with international legal principles.

The amendment "raises potential for a severe impact on international comity", it added, using a phrase denoting respect for a foreign country's legal system.

A U.S. congressional committee has already asked the eSafety Commissioner to testify, accusing her of imperiling American free speech.

The billionaire Musk himself called the Australian social media ban a "backdoor way to control access to the internet by all Australians" in an earlier post on X.

Data published by eSafety and studies since the ban have shown most Australian teenagers under 16 still have social media accounts.

eSafety has said it is preparing a potential enforcement lawsuit against five platforms but is slowed by its limited powers.

The regulator told the panel its currently-limited power to compel documents was at odds with other regulators, making it dependent on "representations from providers about their own compliance".

eSafety also lacked power to compel documents from third-party age assurance providers hired by the platforms, establishing "significant" barriers to the progress of investigations, it added.

DIGI, an industry group representing several platforms, told the senate inquiry eSafety already had extensive enforcement powers that had not been fully tested, and urged greater clarity on whom it could demand documents from.

Google's YouTube and TikTok said in separate submissions there was no known failsafe method to weed out and block underage users.

Parliament has yet to pass the bill for greater enforcement powers. The senate committee will deliver its findings on August 25, after holding hearings.

($1=1.4397 Australian dollars)