Malaysia and Singapore moved on Thursday to speed up competition on the main air route connecting them.
Prime Minister Abdullah Ahmad Badawi gave no details but Malaysia's transport minister said the government would only allow limited budget flights between the two capitals ahead of the planned market opening in January 2009.
The lucrative route is now shared by flag carriers Malaysian Airline System and Singapore Airlines , the world's biggest airline by stock market value.
Malaysia wants to open up the route earlier to AirAsia,which has been lobbying to fly the route Shares in the Malaysian carrier hit a five-month high.
Malaysia Airlines, which is in the midst of a business turnaround, said it was disappointed by the decision.
"We needed time to put Malaysia Airlines strongly on the path of growth as we are working on a number of major initiatives," Managing Director Idris Jala said in a statement. "We will now need to fast track these plans."
The trade union covering Malaysia Airlines warned the government on Thursday that "open skies" could weaken labour standards and urged it to consider such a move carefully.