Low fares carrier Jetstar has been hit with a $545,000 (NZ$595,000) fine from the Federal Court for not always being upfront about booking and transaction fees on its website.
The fine is more than double that imposed on Virgin Australia which accepted a A$200,000 penalty last year for the same "drip pricing" issue.
The Australian Competition and Consumer Commission took action against the airlines in 2014 for "engaging in misleading and deceptive conduct and making false or misleading representations about the price of particular advertised airfares".
In late 2015, the Federal Court found Jetstar had misrepresented fares on its website in 2013, and mobile site in 2014, but other allegations brought by the ACCC were dismissed.
Virgin Australia was found to have made false or misleading representations about fares on its mobile site in 2014 but acted within the law in other instances.