Ryanair’s bid to buy a 24.9 percent stake of Stansted airport could be stopped by the European Competition Commission.

The Competition Commission had indicated in an earlier investigation over BAA’s market dominance, that airlines should only be allowed to hold a tiny percentage of any airport that was later sold.

A challenge from the European Competition Commission would be the second time that the airline has been investigated, with a probe initiated after Ryanair’s bid for Aer Lingus.