The State's largest trade union, SIPTU, wants the Government to extend tax designation to a new terminal at Dublin Airport in which its members hope to invest.

The Dublin Airport branch of the union has circulated formal proposals to set up a new civil aviation terminal investment scheme to buy a 15 to 20 per cent stake in any new terminal.

The union points out that if the terminal was ultimately valued at €600 million, a 15 per cent stake for staff would be worth €90 million.

With 3,000 SIPTU members involved in aviation, this would value each individual shareholding at €30,000, it points out.

The branch believes an investment of €12 million should give the workers at the airport a stake of between 15 and 20 per cent.

However, it hopes any developer would also take into account the particular expertise of the workers when allocating its stake.

"From information received, it is strongly suggested that our investment coupled with our varied airport work experiences could position us to negotiate for between a 15 and 20 per cent shareholding in a second terminal facility," says the SIPTU document.

The document, prepared by senior union officials at the airport, suggests any investment could be made more attractive if tax incentives were provided.

"We would intend to explore, with the Government, the possibility that the terminal project would be tax designated and that any investment would attract significant tax benefits which could mean us having to invest less or look for a greater shareholding," says the document.

The Government has yet to make a decision on a new terminal at the airport, but SIPTU is determined that members locally get some kind of stake in any new venture.

The plan envisages a new company issuing 12 million shares. About 3,000 members would then pay €1,000 a year over four years, thereby realising €12 million.

But the union warns it would only get involved in a terminal with a private developer if there was an agreement in place covering pay and conditions.

It refers to this agreement as a "joint employment procedures and standards agreement".

The union has asked workers at the airport whether they would be interested in getting involved in such a scheme.

It also wants the Irish Congress of Trade Unions to play a crucial role in the new terminal project.

The union acknowledges it is recommending a "paradigm shift", but says this is necessary if the staff are not to "face exclusion from any future meaningful participation in programmes at the airport".