Generic Qantas pictures at Melbourne airport.

Hunt is on for $2 billion in cuts. Photo: Joe Armao

Qantas boss Alan Joyce will face his second Senate inquiry in five days as unions step up their opposition to the scrapping of foreign-ownership restrictions, warning it will lead to a break-up of the airline and the loss of jobs.

Mr Joyce's scheduled appearance on Tuesday night comes after he told a separate Senate inquiry on Friday that Qantas had set up 250 projects to look at ways it could slash costs by $2 billion over the next three years.

Under pressure from unions to reveal more details about planned job cuts, Mr Joyce said the 5000 positions to be axed represented just a quarter of the total cost reductions planned.

Qantas has outlined to unions how it intends to shed about 2500 jobs, which include 1500 from mostly back-office roles and 300 from aircraft maintenance Mr Joyce said the remaining job cuts would be the result of ''fuel, fleet simplification and efficiencies'', citing the retirement of Qantas' Boeing 767 fleet by early next year.

He will appear before the Senate economic legislative committee on Tuesday night in Canberra, which is weighing up the impact on the aviation industry and the broader economy of a relaxation of the Qantas Sale Act.

The ACTU opposes a watering down of the law, claiming in a submission that it would result in the ''probable breaking-up'' of Qantas and the ''possible cessation'' of its international operations.

''Without a requirement for Australian majority ownership … there will be no checks and balances to the wholesale exporting of Qantas jobs in Australia to foreign interests,'' the ACTU said in a submission.

ACTU assistant secretary Tim Lyons will also front the Senate committee on Tuesday night.

An alliance of engineering unions also said in a submission that a preferable option would be for the government to give Qantas a debt guarantee or an equity injection.

The pilots' union favours the removal of the foreign-ownership limits, although it wants to ensure that all airlines comply with the Air Navigation Act in order to gain access to rights to fly in and out of Australia.

The inquiry was set up after the Abbott government dismissed Qantas' pleas for financial assistance, deciding instead to repeal a section of the Sale Act that caps total foreign ownership at 49 per cent, a single investor at 25 per cent and combined holdings by foreign airlines at 35 per cent.

The government faces an uphill battle passing the amendments even when a new Senate chamber sits on July 1, owing to opposition from Labor, the Greens and the Palmer United Party.

But the government has said it has no ''plan B'' and is focused solely on repealing the act.