Alaska Airlines is stepping up pressure on US regulators to determine if rival Virgin America meets US citizenship requirements.

Seattle-based Alaska notes that six months have passed since reports surfaced that US investors sold their stake in Virgin America to UK-based Virgin Group. Shortly afterwards Alaska requested that DOT investigate Virgin America's ownership structure.

US federal law requires US-based carriers to be at least 75% owned and controlled by US investors.

Earlier this year, Alaska twice asked the DOT to investigate Virgin America's ownership, raising concerns echoed by labour and Congressional leaders, most recently by US Senator Patty Murray, chairman of the US Senate subcommittee on transportation, housing and urban development, and representative of Alaska's home state of Washington.

US Congressman James Oberstar, chairman of the US House transportation and infrastructure committee as well the Air Line Pilots Association (ALPA) have also raised questions abut the carrier's citizenship.

However, the DOT has not concluded its review of Virgin America, a department spokesman says, adding there is no expected timeline for a decision.

In the meantime, Virgin America maintains it is compliant with US law and is in contact with regulators.

"Alaska's recent filing is just the latest in another attempt to thwart our increasingly successful and award-winning competition by attempting to raise unfounded concerns over our citizenship. There is nothing new in this petition and nothing has changed with the company's ownership structure to date," a Virgin America spokeswoman says.

Source: Air Transport Intelligence news