Consumers were tricked into believing they were getting a better deal than was possible on Webjet's platform, a lawsuit against the online booking giant claims.
The consumer watchdog on Thursday alleged that Webjet advertised flight deals over a period of five years without telling consumers they'd also be slugged compulsory service and booking fees of up to $54.90.
The statements advertising "flights from" prices were made on its app, in marketing emails on social media and on its website.
Information about the extra fees was included in the app, website and most promotional emails but typically required scrolling and was "not sufficiently clear or prominent", the Australian Competition and Consumer Commission said.
"During this time of cost pressures, many consumers are carefully considering travel arrangements and seeking to save money," commission chair Gina Cass-Gottlieb said.
"A statement about the lowest price must be a true minimum price, not a price subject to further fees and charges before a booking can be made."
In a second tranche of allegations, Webjet is accused of taking payment and "confirming" bookings when it had not booked the flight with the airline.
In these cases, Webjet later allegedly sought additional payment from the consumers to complete the booking or offered the consumer a refund for the flight despite having earlier confirmed the booking.
Some consumers might have paid for other travel arrangements on the basis of the confirmation, forcing them to choose between paying more money or cancelling other arrangements at a potential loss, the commission said.
The 382 related bookings were made between November 2018 and June 2024.
"We are very concerned about this alleged conduct by Webjet, which represented to consumers that their flight booking had been confirmed and left some consumers in the position of having to pay more to later complete the booking," Ms Cass-Gottlieb said.
The case alleging false and misleading representations was filed in Federal Court on Thursday.
Webjet said it had fully cooperated with the commission and it did not believe the issues related to its current pricing and disclosure practices.
"(The company) has already voluntarily and proactively undertaken a number of steps to further improve its disclosure of pricing and fees," it said in a statement.
Millions of customers had booked flights with Webjet over the relevant five-year period but complaints about fees had been very rare, the company added.
The case was taken against Webjet Marketing Pty Ltd, a subsidiary of the ASX-listed Webjet Group.
