Budget airline Ryanair has again been accused of misleading claims by the Advertising Standards Authority (ASA).
Claims against the airline have been upheld in the past
A national advert by the airline read "Robbed by Lastminute.com?", stating that people buying tickets via an online agent were being "ripped off".
The ASA said the advert, which implied online agents overcharged people 100%, could not run "in its current form".
The airline has been forced to withdraw other adverts for breaching ASA rules, including claims over emission levels.
The latest case came after website Lastminute.com said Ryanair's advert, depicting a burglar described as an "online agent", denigrated and discredited their business.
The ASA upheld Lastminute.com's objection that the comparison was misleading, because it quoted prices that were only available to people in the Irish Republic.
The ASA said using Lastminute.ie "did not constitute a relevant comparison for customers in the UK".
It also upheld another complaint against Ryanair by Lastminute, after the airline said the site did not supply terms and conditions and failed to notify customers of changes - neither of which were true.
A spokesperson for the ASA said that despite being criticised, Ryanair had continued to make "equally outrageous claims".
In July, the airline retracted a claim underplaying the role of aviation on the environment.
In a press campaign, the firm said the airline industry represented "just 2% of carbon dioxide emissions".
The ASA ruled it broke rules on truthfulness by not saying the figure was based on global rather than UK emissions.
In August, Ryanair was banned from saying its flight from London to Brussels was quicker and cheaper than the same trip by Eurostar.
It emerged that the airline had not included the time or cost it took to travel to Stansted in the figure.