A draft report said that state-owned Brussels Zaventem Airport is contesting the long-term discounts the airline has with the Charleroi airport, the London Financial Times said.
However, Ryanair said it has not actually seen the draft report, only heard about it through a number of EU Commission sources.
"Airports such as Charleroi have benefited from enormous traffic growth and are now profitable enterprises thanks to Ryanair," said Ryanair CEO Michael O'Leary.
"Why should a complaint from the state-owned, high-cost Brussels Zaventem Airport be allowed defeat competition and low fares?"
Should the company lose this battle it said it will appeal on the basis that the package it enjoys has been offered to a number of other airlines on a non discriminatory basis or work to privatize the Charleroi airport, the Times said.