US secretary of transportation Mary Peters welcomed "a new era where American and Australian consumers, airlines and economies can enjoy the benefits of lower fares and more convenient service," but Singapore Airlines has questioned what is only a partial liberalisation.
The new Open Skies bilateral agreement sees Australia and the United States pledge to lift further restrictions on flights and fares for air travel between the two countries.
Virgin subsidiary V Australia has been granted access to the route under the new rules, but Singapore Airlines has had its request turned down, prompting the carrier to call for greater transparency and competition.
Airline spokesman Stephen Forshaw said: "The Australia-US route is already under-served. There’s a lot of demand that can’t be met and as a result, airfares are far higher than they should be. It’s only through the genuine opening and lifting of restrictions that airfares will fall and consumers will benefit," he explained, adding that Singapore Airlines would not back down from its lobbying campaigns.