The US Department of Transport (DOT) has disapproved on Wednesday the proposed Virgin Blue Holdings Ltd and Delta Air Lines partnership on trans-Pacific service routes, stating that the riding public would be disadvantaged by the carriers' immunity from US anti-trust regulations.

The DOT said that it found no trace of evidence that the proposed alliance would result to sufficient passengers' benefits that would warrant immunity from anti-trust suits, which prompted the regulator's decision to tentatively deny the proposal while giving both companies to respond within the next 14 days.

Despite the emerging hurdle, Virgin Blue informed the Australian Securities Exchange that it remains committed to the proposed alliance, which already got the approval of the Australian Competition and Consumer Commission (ACCC), citing its benefit to consumers by creating an environment for sustainable form of competition.

Also, Delta spokesman Kent Landers stressed that the partnership would deliver benefits to both Australian and US consumers as he added that the company would be "are reviewing the DOT's tentative order and will respond within the comment period."

However, the US transport regulator asserted that both companies were virtual newbies as commercial partners and currently utilise business models that were incompatible.

In its assessment, the DOT concluded that the two airlines "have only just begun to explore the feasibility of arms-length cooperation, much less the degree of cooperation that requires, or would merit, a grant of antitrust immunity."