Malaysia Airlines and AirAsia have been fined for anti-competitive conduct in 2012.
In a statement on Friday, the Malaysia Competition Commission said that the two airlines would each have to pay a penalty of 10 million ringgit ($A3.30 million) for collaborating to integrate some routes in which they earlier competed.
"When businesses agree to share markets, they are agreeing to stop competing, at the expense of the consumers," said commission chairman Siti Norma Yaakob.
AAP reports both airlines said they were reviewing the commission's decision and would respond. They have 30 days to do so.
Both airlines recorded profits in the second half of 2012. However, Malaysia Airlines has been in the red this year while AirAsia has seen sharply lower profits.
MyCC said the penalties were based on revenue earned between January to April 2012 on four routes, and that they equalled less than 10% of their respective worldwide turnovers.