Members of Aer Lingus's biggest union are to be asked to vote on strike action to prevent the airline's management from unilaterally cutting jobs or introducing other changes at the State airline.

SIPTU said last night that it was to hold a protective ballot of its 2,000 members in Aer Lingus for industrial action, and to ask them to support a resolution not to co-operate with any voluntary redundancy deals until there was overall agreement on any future plans for the company.

The union's action is a response to Aer Lingus's latest business plan. This will involve the reduction of 1,325 jobs and the sourcing out of operations such as catering, ground handling and cleaning to independent contractors.

The decision to put the ballot and resolution to members was made yesterday at a meeting of SIPTU shop stewards representing workers in Cork, Dublin and Shannon airports.

The Irish Times understands that Impact, which is the next biggest union in the airline, is to hold a similar meeting today, which is likely to result in a ballot also being put to its members. Impact has already called for all Aer Lingus unions to act together.

A protective ballot means that workers will vote to strike or take some other form of industrial action, if the company unilaterally attempts to push through changes without negotiation.

SIPTU National Industrial Secretary Mr Michael Halpenny said last night the ballot aimed to pre-empt any attempt by management to force through change.

He also made it clear that the union opposed compulsory redundancies. "There has been a lot of media speculation on compulsory redundancies," he said. "I want to make it clear now that not only will there be no compulsory redundancies, there will be no compulsory anything."

Aer Lingus spokespersons were unavailable to comment last night.

A cabinet sub-committee is currently considering the future of Aer Lingus and is due to report to Government in the autumn.