Australia's eSafety commissioner has issued legal notices to Apple and Meta - the parent company of WhatsApp, Facebook and Instagram.
Microsoft, including its Skype platform, Snap and Omegle also received notices.
The move is under the Online Safety Act 2021 and requires the companies to report on how they are tackling the proliferation of child sexual exploitation material.
The act, described as a "world-leading tool" by eSafety Commissioner Julie Inman Grant, has basic online safety expectations, setting out minimum requirements for tech companies that wish to operate in Australia.
"They will help us 'lift the hood' on what companies are doing - and are not doing - to protect their users from harm," she said in a statement.
"As more companies move towards encrypted messaging services and deploy features like live streaming, the fear is that this horrific material will spread unchecked on these platforms."
Ms Inman Grant said the decision to issue a notice was an information gathering process.
Companies who do not respond within 28 days could face penalties of up to $555,000 a day.
Microsoft confirmed the company will respond and Meta says it is reviewing the notices.
"The safety of our users is a top priority and we continue to proactively engage with the eSafety Commissioner on these important issues," a Meta spokesperson said in a statement to AAP.
The eSafety regulator has handled more than 61,000 complaints about illegal and restricted content since 2015, with the majority involving child sexual exploitation material.
A report released in February found 11 per cent of Australians aged 14 to 17 reported being asked by someone on the internet to send a sexual image of themselves.
AAP has approached all tech companies involved for comment.
