The airport branch of SIPTU, the State's largest union, is preparing a radical new proposal which could result in its members financially investing in a new terminal at Dublin Airport.

SIPTU staff at the airport will be briefed on Friday on the idea which could see the union's members investing more than €12 million in a second terminal. The union's branch has written to 13 companies that previously indicated to Government a willingness to build a second terminal.

The union has proposed entering "dialogue" with these companies on a potential commercial venture. Under the proposals, staff at the airport would pay into a civil aviation investment scheme. The funds in this scheme would ultimately be used by workers to purchase a stake in any new terminal.

The Dublin Airport Authority (DAA) might also be a party to the arrangements, although it declined to comment yesterday.Under the draft proposals drawn up so far, SIPTU might take a stake of between 12.5 and 16 per cent in any terminal. It is possible other unions at the airport could become part of the project at a later stage.

The issue of a second terminal competing with existing facilities has resurfaced in recent days, following remarks by the Minister for Transport, Mr Cullen. He recently said in a television interview the issue was being examined and a decision on whether to proceed would be taken shortly.

The idea of a second terminal at Dublin Airport had strong support from the last minister for transport, Mr Brennan, but unions have traditionally opposed the idea.

Among the companies keen to get a second terminal underway is Omega Air, owned by the businessmen Ulick and Desmond McEvaddy. They own a large land bank near the airport and have repeatedly spoken of their desire to get the project up and running. It is understood the McEvaddy brothers have held discussions with SIPTU over recent months.

The details of the proposal have been discussed with the president of SIPTU, Mr Jack O'Connor. On Friday, local branch representatives will ask permission of members to develop the proposals further and enter serious negotations with some of the 13 companies. It is understood three unnamed companies have already agreed to negotiate with the SIPTU branch. Union sources last night said there could be no compromise on pay levels with any new terminal operator.

The SIPTU meeting on Friday will also consider the ending of discounted flights for Dublin Airport Authority staff on Aer Lingus flights. This practice where airport staff (formerly of Aer Rianta) could take up unfilled seats on Aer Lingus flights is due to end soon.