VIRGIN Blue's long-haul offshoot, V Australia, could have to wait at least another six months for a ruling from American authorities on its proposed tie-up with Delta Air Lines because of a tougher stance on airline alliances in the US.

Any delays to the ruling will be a blow to V Australia because it is counting on the planned revenue-sharing agreement with the world's largest airline to limit its losses on the highly competitive trans-Pacific route.

Hubert Horan, an American aviation consultant who worked on the original merger proposal between Qantas and Air New Zealand in the 1980s, said the Virgin deal had been caught up in the imbroglio in the US over an application from American Airlines and British Airlines to pool trans-Atlantic flights to London's Heathrow Airport.

''There is a real stalemate [over the proposed BA-American Airlines alliance], which means there is not going to be a ruling on Delta and Virgin any time soon,'' he said.

''[The Delta-Virgin deal] is caught up in the wider dynamics … there is a serious political catfight.''

Virgin Blue spokeswoman Heather Jeffrey said a response was not expected until June from the Transportation Department, which she believed was ''still in fact-finding phase''.

The Australian Competition and Consumer Commission last month gave tentative approval for Virgin to pursue a tie-up with Delta Air Lines on flights between Australia and the US. But it has kept the two airlines on probation by proposing to grant them immunity from anti-competition laws for just three years.