Ryanair has warned that it intends to take legal action aimed at preventing Aer Lingus from making additional contributions to its pension scheme. Ryanair is Aer Lingus's largest shareholder, with a stake of more almost 30%.

In an open letter to all Aer Lingus shareholders, Ryanair said it was "deeply worried" by the airline's stock exchange statement earlier this week.

Aer Lingus said on Monday that it was in talks with unions over how to fill a hole in its pension scheme of at least €400m, even though it said it had no legal obligation to contribute.

Ryanair's letter said it intended to start legal proceedings because it had failed in its bid to hold an EGM of Aer Lingus shareholders to discuss the issue.

Meanwhile, Ryanair says it carried 4.39 million passengers in January, down 6% from the same month last year. The load factor, or percentage of seats filled, was unchanged at 71%.