SYDNEY, Australia — A new law in Australia gives law enforcement authorities the power to compel tech-industry giants like Apple to create tools that would circumvent the encryption built into their products.

The law, the Telecommunications and Other Legislation Amendment (Assistance and Access) Act 2018, applies only to tech products used or sold in Australia. But its impact could be global: If Apple were to build a so-called back door for iPhones sold in Australia, the authorities in other countries, including the United States, could force the company to use that same tool to assist their investigations.

The Australian law went into effect last month. It is one of the most assertive efforts by lawmakers to rein in tech companies, which have argued for decades that unbreakable encryption is an imperative part of protecting the private communications of their customers.

In recent years, law enforcement officials have complained that tough encryption has made it impossible for them to gain access to the online discussions of crime suspects, particularly in time-sensitive terror investigations.