In March, Qantaslink began flying from Albury to Melbourne, offering eight flights a week.

Rex has welcomed the Australian Competition and Consumer Commission investigation, arguing that some regional routes could barely support one provider, let alone two.

According to figures supplied by Rex, the airline's Melbourne to Albury service averaged 1845 monthly passengers pre-COVID.

In the four months to April 2021, the service averaged just 373 passengers in a month.

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Rex deputy chairman John Sharp claimed the presence of another service would spell huge losses for both his airline and Qantas.

"Even at pre-COVID levels, these routes could not sustain two carriers running a full regional schedule, which explains why Qantas did not enter these routes in the last 20 years," he said.

In April, Mr Sharp wrote to ACCC's chairman Rod Sims asking him to intervene.

However, a Qantas spokesman hit back at the suggestion they were embarking on a deliberate loss-making operation, saying there was still profit to be had on regional routes.

"We don't start routes if we don't think they will be commercially viable for us. In fact, in the second half of calendar year 2020, 99 per cent of the time we were able to fly, we generated positive cashflow," he said.

Earlier this year, prior to Rex writing to him, ACCC chairman Rod Sims told a senate inquiry he did not believe Qantas was engaging in predatory behaviour.

"If Qantas has the aircraft, it's incurring the fixed costs, it realises it can make a cash contribution by flying somewhere - it's a bit hard to call that predatory," he said.

In direct retaliation to Qantas' recent moves on Rex routes, the regional carrier has flagged plans to "soon" expand services to other regional ports currently solely serviced by Qantas.