A fight between Qantas and Canberra Airport has escalated dramatically, with the airline releasing an email suggesting a plane was held to "ransom", and chief executive Alan Joyce comparing the airport's behaviour to that of Somali pirates.

In response to Mr Joyce's claims of an $18,000 ransom requested by credit card, Canberra Airport managing director Stephen Byron responded incredulously: "Do these people walk around with a credit card machine?"

In an interview with ABC Canberra, Mr Byron said the airport had "absolutely not" requested payment before the plane was allowed to leave, after it was diverted to Canberra in March 2017.

But according to an email and invoice supplied to the ABC, a sum of $20,503.77, including GST, was requested with the email reading: "Please note the aircraft cannot depart until the invoice is paid."

The ABC has not been able to independently verify the documents, which support Qantas' claims that the airport asked for money to be paid before the plane could depart.

The email requests payment by credit card.

An email sent to Qantas requesting payment before the plane could depart Canberra airport. ( Supplied )

The stoush revolves around a plane that was diverted from Sydney and landed in Canberra, and was physically prevented from leaving when a car was parked behind it.

Canberra Airport contends Qantas had been causing safety hazards by diverting flights to it without proper planning, but Mr Joyce compared the tactics to Somali pirates.

"They actually ransomed one of our aircraft, I mean talk about appalling behaviour," he said.

"I've never seen it in my nearly 30 years in the aviation industry where a pilot's been told to pass over a credit card of $18,000 otherwise the aircraft can't go.

"Maybe the airport should be called the Canberra Pirates, because you wouldn't have this in Somalia."

Mr Byron said that was incorrect, though admitted a car had been parked behind a Qantas jet.

Canberra Airport said the stoush began over Qantas diverting too many flights. ( ABC News: Jana Black )

He said the incident only lasted for eight minutes.

"Qantas had landed two 747s unannounced and put other aircraft in danger, five weeks before this incident," he said.

"This was an incident where Qantas had to be held to account in terms of safety and putting other aircraft at risk.

"There was no payment made at all, there was no dispute about payment.

"This was the last in a series of multiple incidents where unannounced, Qantas were diverting large international aircraft to Canberra Airport, and putting other aircraft that had planned and arrangements in place to divert to Canberra Airport in jeopardy.

"It is true that we said we want a dialogue before the plane leaves and a commitment that these unauthorised landings do not occur again and we got that commitment."

Better arbitration called for

Tension between the companies has been brewing for weeks, with Mr Byron campaigning against the high cancellation rates of domestic Qantas flights between Sydney and Canberra.

Mr Joyce's position was backed up by former Australian Competition and Consumer Commission (ACCC) head Graeme Samuels, who said the position airports held amounted to a monopoly.

"That's not Australia, that's a third-world country," he said.

"In fact, I'm assured by Qantas that doesn't even happen in third-world countries."

But Mr Byron said safety had always been the airport's priority, calling Mr Samuels a "well-paid lobbyist" for Qantas' interests.

"Canberra Airport can't handle multiple diversions, Qantas was putting too much pressure with their diversions," he said.

"Qantas was running roughshod over all the other airlines and Canberra Airport, making up its own rules and putting other aircraft in danger."

Mr Joyce called for better arbitration between airlines and airports, and accused airports around the country of passing costs onto airlines and consumers.

"We think an arbitration role that the ACCC can fulfil where the airlines and airports can get to agreement, it forces them to go in and do arbitration," he said.

"Consumers are losing out, because there's hundreds of millions of dollars in higher charges that we can't pass on to our customers.

"They can just sit back, increase the fees, and let the airlines pay for it."

According to Mr Byron, Qantas and the airport had agreed to an effective ceasefire over the incident, until Mr Joyce's comments last night.