Aer Lingus chief executive Dermot Mannion will seek to persuade the airline's workers of the merits of privatisation and pensions at staff meetings over the next few weeks. Last night Mr Mannion's request to address a Siptu meeting was turned down.

Mr Mannion submitted a late request to address the meeting which was attended by hundreds of Siptu members. Siptu representatives told him it was a private meeting and last night Mr Mannion said "I respect that".

However he now intends to talk to staff at meetings at the airport. He will seek to sell the idea that a privatisation process could present a "once in a lifetime" opportunity to address the Aer Lingus pension which is facing a deficit of over €300 million. Staff from the Dublin Airport Authority (DAA) and SR Technics are also members of the scheme.

The break-up of this multi-employer scheme is likely to be one consequence of the Aer Lingus sale process. Most observers regard the looming pension deficit as the biggest obstacle to getting agreement on a sale process.

Last night SIPTU members decided to endorse the anti-privatisation campaign conducted by the union and to continue to engage with the Minister for Transport and the company on core issues such as job security and pensions. The union said last night it would conduct a protective ballot for industrial action in the event of the company unilaterally moving on core issues of concern to members.

While Siptu is strongly opposed to a flotation or private placement, Impact, the other main union at the airline, appears more willing to at least hear the case for privatisation. The different approaches of the unions has been remarked upon in industrial relations journals.

While the airline itself favours a June sale, this might not be possible to achieve if the Cabinet does not sign off on the process soon. The issue may surface at next Tuesday's Cabinet meeting.

If the June date is missed, most observers believe a sale would then take place some time in September. While Minster for Transport Martin Cullen has re-iterated his support for a sale, the Taoiseach's position is harder to discern.

Political sources believe the softer tone coming from Impact may embolden Ministers to make a decision soon. Impact, which represents 1,800 Aer Lingus staff including cabin crew, pilots and middle managers, this week set out five "tests" which needed to be met in advance of any flotation.

It said any sale must result in substantial expenditure on additional aircraft and must also yield sufficient investment in staff pensions to ensure that current benefits are maintained.

The union also wants outstanding pay issues involving pilots and other staff settled; it is seeking to have a now completed profit-sharing scheme extended; and it wants guarantees on collective bargaining arrangements and job security "in a post-flotation Aer Lingus".

Impact deputy general secretary Shay Cody said any flotation would be "worse than pointless" if the funds raised did not translate into more and better planes.

At present staff own 14.9 per cent of the airline and if the company achieves a high valuation staff may stand to make a substantial sum of money - at least on paper.

For example, if Aer Lingus was valued at €1 billion, the staff shareholding would be worth almost €150 million. This would translate into €43,165 per employee. Aer Lingus recently said it was employing aproximately 3,475 people. The value of the shareholding is based on the staff retaining their 14.9 per cent stake following the sales process.