Australia's Sydney Airport has lashed out at warnings by its Brisbane rival that the privatisation of Qantas could reduce competition among airports, describing the allegations as offensive and unfounded.

Brisbane Airport Corp last week joined Virgin Blue in raising questions about Macquarie Bank's role as a dual stakeholder in the airline and Sydney Airport if the AU$11.1 billion takeover proceeds.

BAC asked how the commission would ensure there would not be greater concentration of air services through Sydney Airport at the expense of other states in Australia, and called on the Australian Government to remove access restrictions on all airports except Sydney Airport if it approved the deal.

Macquarie is proposing a 14.7 per cent holding in the airline and owns 18 per cent of Macquarie Airports (MAp), which owns 58.8 per cent of Sydney Airport.

MAp says this translates to a 10.13 per cent stake in the airport, and the bidder consortium, Airline Partners Australia (APA), contends the deal is so structured that it meets all cross-ownership requirements which restrict anyone with a stake of more than 5 per cent in an airport operator company owning more than 15 per cent of an airline.

But BAC warned the Qantas takeover could result in competitive pressures and incentives that could reduce factors that limited the abuse of market power by airports.

It warned the incentive to engage in anti-competitive conduct "may be heightened" as a result of the acquisition.

Sydney Airport's chief executive rejected out of hand any suggestion that Sydney Airport would have a heightened incentive to engage in anti-competitive conduct.

"This is an offensive allegation," Russell Balding said. "I have a clear obligation as CEO and as a director of SACL to act in accordance with relevant laws.

"I understand that Brisbane Airport is trying to further its own commercial interests, but smearing competitors is not an appropriate way to further its case."

Mr Balding also questioned a call by BAC to remove airline access restrictions on all major airports except Sydney. Access to Sydney, Brisbane, Melbourne and Perth airports are currently subject to restrictions and bilateral negotiations between the Australian and foreign governments.

He said the 1998 Productivity Commission recommendations cited by BAC referred to removing restrictions at secondary airports on a reciprocal basis.

"The Productivity Commission was recommending that there should be unlimited capacity between Melbourne and Milan, not Rome; between Adelaide and Stansted, not Heathrow," Mr Balding said.

"Sydney Airport has not sighted BAC's submission, but it would be mischievous if it represents the Productivity Commission as recommending that Sydney Airport be tied up in red tape while advocating 'open skies' for provincial Australian airports."

Members of the APA consortium, which released a bidder's statement on Feb. 2, also rejected suggestions that Macquarie Bank's dual role would lead to collusion between Qantas and Sydney Airport.

Shareholders have until March 9 to accept the AU$5.60 per share cash deal and have been warned there will be no follow-on offer if the consortium fails to reach the 90 per cent acceptance needed to compulsorily acquire the shares of any hold-outs.

Qantas will put out a target's statement and an independent report after releasing its half-yearly results on Feb. 8.