Virgin Blue founder Richard Branson has come out strongly against the decision not to allow the airline to enter an alliance with Air New Zealand on transtasman routes.

Sir Richard said he wanted to compete on a level playing field but Australia's competition regulator wasn't making business easy.

Sir Richard was in Melbourne yesterday to mark the carrier's 10th birthday, admitting "a couple of setbacks" had cast a shadow over the celebrations. "But nothing that we won't be able to overcome," he emphasised.

Virgin Blue's share price tumbled last week after the Australian Competition and Consumer Commission blocked a proposed alliance with Air NZ on the transtasman route.

The rejection came only a day after the regulator refused to approve a partnership between Virgin Blue and American carrier Delta Air Lines on Australia-US services.

"Qantas have a relationship with South African Airways the same week that a very small airline, Virgin Blue, is told we can't have relationships with Delta or Air NZ," Sir Richard said.

"All we're saying to the regulator is: do to Virgin as you do to Qantas and be fair."

- AAP