"These fees applied to the substantial majority of online bookings and should have been disclosed upfront and prominently with or within headline prices," an ACCC spokesman said.

Virgin Australia questioned why only two airlines were being targeted, when the "drip-pricing" method and the separate booking and service fee were part of a "long-standing" practice among "all" Australian airlines.

"We welcome an industry-wide approach to booking and service fees to ensure consistency across all airlines," a spokeswoman said. "We are currently reviewing the proceedings commenced by the ACCC and will be considering all options."

But ACCC chairman Rod Sims defended the action, saying the majority of complaints were about Jetstar and Virgin.

"This is part of a broader investigation," he said., "We're looking into other industries as well in relation to drip pricing, but it's driven by what we perceive as the most egregious behaviour.