Jetstar and Virgin have been fined hundreds of thousands of dollars after they were found to have advertised "false and misleading" flight prices.
The Federal Court on Tuesday ordered Jetstar Airways to pay $545,000 and Virgin Australia Airlines to pay $200,000 for breaches of Australian Consumer Law.
The penalties come after the court found in 2015 that the use of "drip pricing" by the airlines was misleading and deceptive.
Drip pricing is where a headline price is advertised at the beginning of an online booking but extra fees and charges are introduced as it progresses.
Jetstar accepted the court's decision on Tuesday, noting it had made changes to its web and mobile sites so its booking process was clearer to customers.
"These changes, made in 2014 were previously found to be satisfactory by the Federal Court," it said in a statement.
"On 1 September 2016 we removed the booking and service fee on domestic and international flights from Australia and we continue to offer a number of fee-free payment options for our customers who prefer not to pay with a credit card."
The Australian Competition and Consumer Commission launched the Federal Court proceedings in 2014, arguing that extra fees should be disclosed upfront and prominently.
ACCC chairman Rod Sims said in a statement on Tuesday that businesses across several industries were now adequately disclosing extra fees and charges, as a result of the watchdog's work.
WHY JETSTAR AND VIRGIN AUSTRALIA HAVE BEEN FINES:
* Federal Court proceedings were launched against the airlines in 2014 by the Australian Competition and Consumer Commission, which argued they were advertising prominent headline prices without adequately disclosing booking and service fees.
* Jetstar and Virgin had argued that fees were adequately disclosed before customers entered into binding purchases.
* The court found in 2015 that the airlines' use of "drip pricing" was misleading, deceptive and contravened Australian consumer law.
* On Tuesday the court issued its punishment, ordering Jetstar to pay a $545,000 penalty and Virgin Airlines to pay $200,000.
HOW DRIP PRICING WORKS:
* Drip pricing is where a headline price is advertised before an online purchase but extra fees and charges are introduced as the transaction progresses, according to the ACCC.
* For example, a customer might click on a flight advertised for $139, only to find when they reach payment that a $17 credit card booking and service fee applies.
* The ACCC says businesses can apply fees and charges but they cannot mislead you into paying these fees without telling you up front how much they will cost.