Ryanair has accused BP of using its monopoly to increase the cost of aviation fuel by over 50 per cent at Belfast City and Glasgow Prestwick airports.
The budget airline has written to the Office of Fair Trading asking for action on "profiteering" as BP Air has a monopoly on both of the airports.
Ryanair's director of legal and regulatory affairs, Jim Callaghan, said: "Air BP has a complete monopoly on the supply of aviation fuel at these airports and is abusing this position to unilaterally impose over 50 per cent cost increases (over ten times the rate of inflation) for the delivery of aviation fuel.
"At a time of recession, when consumer confidence is collapsing, this kind of blatant abuse by a massively profitable oil company cannot be accepted."
The Irish airline said Air BP has claimed the increases are due to 'the rising cost of oil' but Ryanair argues the oil firms are already making enough profits from the high oil prices.
A BP spokesperson denied the company has a monopoly and said airlines can choose to refuel elsewhere and there is fierce competition between suppliers and airlines.
"We believe the prices offered to Ryanair are reasonable and we are confident they do not breach any competition law," the spokesperson said.
BP said it is "surprised" Ryanair has chosen to involve the competition authorities in ongoing commercial negotiations, but said if it is contacted by the OFT BP will cooperate fully.