Ryanair has warned that it will not get involved in any new terminal at Dublin airport if the trade union Siptu has a shareholding in the project.

Speaking at a press conference in Dublin, the airline's chief executive, Michael O'Leary, said of Siptu: "Even with a small shareholding in the project, we wouldn't go near the place."

"This is the union that, when they didn't like Séamus Brennan's plans, they closed the main airport in this country twice in two years," he said.

He said Siptu didn't want competition in any sphere and had blocked taxi and bus deregulation.

His comments come at a time when Siptu is considering taking a shareholding in a terminal project, with either the Dublin Airport Authority or the McEvaddy brothers.

However, Mr O'Leary said the company might be prepared to use a terminal involving the Dublin Airport Authority (DAA), formerly Aer Rianta, but it would not be able to offer the full range of new services and new jobs under such an arrangement.

Referring to the DAA, he said: "They are the worst builders of inefficient terminal facilities since Wilbur and Orville first flew."

Asked what would happen if the DAA was involved, he replied: "Instead of us delivering between five and 10 million new passengers over a five-year period, I think we'd deliver between half and one million over a five- to 10-year period."

He has asked Ryanair customers, via www.ryanair.com, to e-mail the Taoiseach on the issue of the terminal. He said the airline was offering 100,000 free seats to passengers who e-mailed the Taoiseach asking him to give permission for a new terminal.

Mr O'Leary said that he now feared a fudge on the issue. "What we don't want, and what we would strongly oppose, is no competition. And no competition is what Bertie and the fudge meisters in the Cabinet are going to give us, which is some waffley fudge that Dublin Airport Authority or Siptu would be developing the second terminal.

"The second terminal, run by the same people who delivered us the black hole of Calcutta, known as the first terminal, would not represent competition."

He said a site on the north apron was by far the best location for a terminal but this did not preclude a third terminal on land owned by businessmen Ulick and Desmond McEvaddy.

"We believe they should be allow to build a terminal on that site as well, but not at the expense of an efficient low-cost terminal on the north apron site," he said. "Don't make it the second terminal, make it the third or fourth terminal," he added.

"As the second terminal, it would be a disaster," he explained.