An alliance of trade unions launched a joint campaign in Melbourne to save thousands of Qantas engineering jobs at risk as the airline reviews its maintenance operations in Australia.

While the licensed aircraft engineers' union fears a decision has already been made to axe the Tullamarine workshop, three other unions -- the AMWU (Australian Manufacturing Workers Union), the AWU (Australian Workers Union) and the ETU (Electrical Trades Union) -- have joined forces to lobby the federal and state governments, and the airline, to help save local jobs.

Qantas plans to consolidate three maintenance bases -- two of which are in Victoria (at Tullamarine and Avalon airports), the other at Brisbane airport -- into one or two bases, with a decision to be made by mid-April.

AMWU Assistant National Secretary Glenn Thompson warned the unions would lobby governments to fight for the jobs of 6000 Qantas engineering employees and 350 apprentices.

"We are committed to ensuring that ongoing skills and training, and quality hi-tech jobs are maintained," Mr Thompson said.

"We are seeking to have some discussion with Qantas, about infrastructure spending to deal with the challenges that Qantas Engineering is facing into the future."

AWU Victorian Secretary Cesar Melhem said he feared "hundreds" of jobs could go in the first round of cuts.

"I'm throwing a challenge to [Victorian] Premier [Ted] Baillieu ... to come out and start working with Qantas ... to retain bases in Victoria," he said.

"We understand there will be some job losses as part of the first review, but we don't want to lose the rest of the workforce in the next few years."

But a Qantas spokesman said the introduction of new aircraft "has seen a significant reduction in the amount of heavy maintenance required on our fleet".

"We need to consolidate our three heavy maintenance bases Australia into two or one and are consulting with unions and our employees," the spokesman said.

Mr Melhem said it was "absolute crap" that Qantas' new planes, including the Airbus A380 superjumbo and forthcoming Boeing 787 Dreamliners, would not require heavy maintenance in Australia, despite what the aircraft manufacturers might officially say about the aircrafts' service intervals.

"If Qantas want to keep calling Australia home, you've got to maintain your fleet at home," Mr Melhem said.

"We've commissioned studies to put the case to Qantas and the federal ... and state governments to put in place a plan to keep the jobs here," he said.

ETU assistant national secretary Allen Hicks said it would be a "disgrace" if jobs were lost to overseas.

"Qantas has that safety record for one clear reason: and that's because of ... the workers who have looked after this industry and this airline for so long," he said.

But a Qantas spokesman said the airline did 90 percent of its maintenance and engineering in Australia, the only airline to do so.

"We have made it clear that we will not be sending any work that is currently done at our Australian bases offshore," he said.

Separately, the union representing Qantas aircraft engineers suspects the airline's management has already decided to axe its Tullamarine heavy maintenance workshop - a move that would see 400 jobs lost, and more to follow.

"The signals we're receiving are all leading to them closing down Tullamarine this year and only giving Avalon enough work for another three-or-so years," said Steve Purvinas, the federal secretary of the Australian Licensed Aircraft Engineers Association.

Mr Purvinas said it made no sense for Qantas to shut its Tullamarine workshop, which carries out heavy maintenance on the airline's 71 Boeing 737s.

"I don't know why anyone in their right mind would want to close down the most efficient 737 facility in the world," he said.

One option Qantas has put to the union could see the transfer of maintenance work on the older B737s to nearby Avalon, which also works on Qantas' ageing Boeing 747 jumbos, Mr Purvinas said.

But that would be only a short-term reprieve for the 700 Avalon workers, he said.

"They've got the 747 aircraft that are ultimately going to retire - if they give them all the old retiring aircraft then in a few years they'll be coming back saying: 'We don't have enough work to keep it open. Sorry, off you go'," Mr Purvinas said.

"It would be 400 [jobs lost] at Tullamarine later this year and 600 or 700 at Avalon in a few years' time."

Qantas told The Age that no decision had been made.

"We haven't made a decision and we are continuing to consult with our employees, unions and the Federal and state governments. A decision will not be made until after the consultation period ends in mid-April," a Qantas spokesman said.