Virgin America said Tuesday that it still complied with rules governing foreign ownership of U.S. airlines as it sought to halt efforts to ground the carrier.

The Transportation Department faces calls from Alaska Airlines Group Inc. (ALK) and two industry unions to ground the Burlingame, Calif.-based airline founded by Sir Richard Branson unless it discloses more details of its ownership.

The Wall Street Journal reported earlier this month that the two U.S. hedge funds drafted in to provide start-up capital - and meet the ownership test - had cashed in their holdings.

Virgin America insisted in a regulatory filing that it complied with all "citizenship" rules to operate a U.S. carrier and that "no sale or transfer of the 75% U.S. citizen controlling equity ... had occurred."

The airline did not say whether U.S. investors retained an "economic interest" alongside board representation, which its opponents said was critical to meet the citizenship test.

Virgin America also did not identify who held the U.S.-owned shares. It is understood to be seeking alternatives to the two founding investors.

While the airline asked the DOT to dismiss the calls for a fresh probe into its ownership - and potential grounding - the Air Line Pilots' Association and the Association of Flight Attendants-CWA both called for the department to take action.

-By Doug Cameron, Dow Jones Newswires; 312-750-4135; doug.cameron@dowjones.com