Ryanair is suing Google in Ireland following repeated requests to remove travel comparison site eDreams from search results for the airline.
The Irish budget carrier claims eDreams is misleading customers due to similar website layouts.
It follows a successful move by the airline in Germany, resulting in Google removing eDreams from results.
Ryanair said it has repeatedly called on Google to stop selling advertising to eDreams.
Chief executive of Ryanair Michael O'Leary said: “All we want is for eDreams to stop duping consumers and advertise honestly.”
According to the airline eDreams has been doing this for up to 18 months but Ryanair claims there has been a surge in customers asking it about eDreams in the past year.
Ryanair is also taking legal action against eDreams itself to prevent it from using similar branding.
In a statement eDreams said: "The case against Google and eDreams has only just been filed so there is little we can say beyond the fact that we disagree strongly with Ryanair’s position. This action is clearly just another attempt from Ryanair to stop Online Travel Agencies from offering consumers the best price and choice when it comes to booking flights."
EDreams, based in Spain, is headed up by ex-EasyJet chief of of operations Dana Dunne.
The budget airline has recently reported record passenger numbers as well as soaring profits.
Ryanair's chief marketing officer Kenny Jacobs said: "Both the subdomain eDreams uses and the branding and design it uses on its site, are a deliberate attempt to dupe consumers into thinking they're directly booking with Ryanair."