The Australian Competition and Consumer Commission is launching action in the Federal Court claiming Qantas engaged in false, misleading or deceptive conduct after continuing to sell the tickets for an average of more than two weeks, and up to 47 days in some cases.

It’s also alleging the airline didn’t notify existing ticket holders for 10,000 flights that they had been cancelled for an average of 18 days, and up to 48 days, between May and July 2022.

This left customers less time to make alternative arrangements and may have led them to pay higher prices.

The ACCC said Qantas continued to sell tickets for the flights on its website for two days or more and delayed informing ticketholders their flights were cancelled for the same period of time for about 70 per cent of cancelled flights.

Qantas cancelled a quarter of its flights between May and July 2022, which amounted to about 15,000, the ACCC said.

Chair Gina Cass-Gottlieb said the commission had conducted a detailed investigation into the airline.

“As a result, we have commenced these proceedings alleging that Qantas continued selling tickets for thousands of cancelled flights, likely affecting the travel plans of tens of thousands of people,” she said.

“This case does not involve any alleged breach in relation to the actual cancellation of flights, but rather relates to Qantas’ conduct after it had cancelled the flights.”

The ACCC is seeking penalties, injunctions, declarations and costs.

Qantas said in a statement it took the allegations by the ACCC seriously.

“We have a longstanding approach to managing cancellations for flights, with a focus on providing customers with rebooking options or refunds,” it said.

“It’s a process that is consistent with common practice at many other airlines.”

It noted the period examined by the ACCC was a “time of unprecedented upheaval for the entire airline industry”.

“We will examine the details of the ACCC’s allegations and respond to them in full in court.”

Treasurer Jim Chalmers said they were “deeply concerning allegations”.

“This is the consumer watchdog doing its job and a reminder that businesses need to do the right thing by people – breaches of consumer law carry heavy penalties,” he said in a statement.

The government has initiated a competition review and aviation white paper to identify issues in the sector which need fixing.

The federal opposition is also pursuing the government over a decision to block Qatar Airways from boosting the number of flights into the country – a move described by critics as protecting Qantas.

Qantas has also come under fire after it was revealed it lobbied the federal government to block the bid.

The government decision prompted a backlash, with Virgin Australia saying the extra services would have led to lower airfares and the government should not be protecting the profits of a publicly-listed company.

-with AAP