The US Justice Department has launched an investigation to look into possible collusion among major US airlines to limit available seats to keep airfares high, according to the Associated Press. The move by the US authorities was made on the same day that Dubai flag carrier Emirates airline hit back at allegations of unfair competition levelled at Gulf airlines.

Civil investigative letters were sent out to the major carriers including Delta, United and American Airlines on 30 June. The letters, according to the report, demanded copies of all communications between the airlines with Wall Street analysts and major shareholders about their plans for passenger-carrying capacity.

The Justice Department is looking to pin down any communications implying the undesirability for the airlines to increase capacity. The agency is looking at a time frame that began in January 2010.

Official spokesmen from the Big 3 confirmed receiving the letter and plans to comply.

US Senator Richard Blumenthal requested the investigation in the wake of the annual general meeting of the International Air Transport Association (Iata), held in June in Miami, where the airlines are understood to have openly discussed capacity.

The Justice Department acted on the request to ensure consumers are not hurt by less competition resulting from mergers or alliances. It had tried but failed to block a merger between American Airlines and US Airways in 2013.

Wall Street analysts have not kept secret their opinion that airlines should not expand their capacity faster than the US economy to maintain a strong financial performance. The US airline industry has kept up with this trend since 2010, intensifying lawmakers’ suspicions that a collusion could exist not just among the airlines but with Wall Street analysts as well.   

Emirates airline’s CEO Tim Clark was in Washington in late June to present his airline’s formal rebuttal to allegations made by the Big 3 that it has received unfair subsidies from the government. Clark stressed that the Big 3’s request for their government to review the open skies bilateral agreement and possibly unilaterally freeze the Gulf airlines’ US expansion plans could only work against the US aviation industry’s interests.