Last month, NI Environment Minister Edwin Poots decided to put the controversial matter to public inquiry, following a campaign by residents living near the airport.
The residents claim the extension will increase noise pollutions in the area.
Mr O'Leary said his company's plans for up to 500 new jobs and up to five more air routes to Europe from the airport are now at risk due to the delay.
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Mr O'Leary said: "They have devolved decision making powers here in Northern Ireland and the first decision they have taken is to fudge this off to a public inquiry. We are used to that in Dublin but we had higher hopes for the independent thought and political action here."
However, DUP leader and Northern Ireland First Minister Peter Robinson has rounded on these comments, saying: "Michael O'Leary might be used to bullying his long-suffering customers but he cannot bully the people affected by the proposed extension of the Belfast City Airport runway.
"Public consultation designed to allow local people to have their say will determine the direction that this proposal takes. My constituents have the absolute right to make their views known on this issue and they will not be bullied by Michael O'Leary on this or any other issue."
Mr O'Leary has claimed that other European countries are benefiting from new aircraft and routes as a result of the lack of a runway extension at the Belfast airport.
(NS/BMcC)
