The court found the advertisement made misleading or false representations that the online booking service had benefits it did not and therefore was likely to deceive customers.

That was because many people showed up to the car parks after booking online only to find there was nowhere for them to park.

Secure, which is majority-owned by a Japanese firm and operates more than 600 car parks across Australia, was ordered to pay a fine of $10.9 million within 30 days.

The penalty sent a strong message to all businesses that making false or misleading claims would attract hefty consequences, ACCC commissioner Liza Carver said.

“Customers may have been seriously inconvenienced when they arrived at their chosen car park to discover the parking space they thought they had booked was not available to them," she said.

Secure admitted that it generally did not reserve the spaces and customers would arrive to a full car park at times.

Its Secure-a-Spot online booking service was advertised on Secure Parking's website, social media and promoted directly to customers via email.

Promotions included phrases like: "Book online for a guaranteed spot."

The business has since rebranded the service to: "Secure Parking - Book Online".

For the 90 days following the judgment, the Secure Parking homepage will have to display a click-through icon for the public to access information about the company's breach of consumer laws.

The court also ordered the company to pay ACCC's legal costs as well as reviewing and maintaining its existing compliance program.

Secure Parking has been contacted for comment.