Delta Air Lines says it is “deeply disappointed” with a new U.S.-Japan aviation deal reached this week, which the airline contends could threaten its hub in Japan and its Atlanta-Tokyo nonstops.

The pact is a blow to Delta management and outgoing CEO Richard Anderson, who had derided the deal as “dark skies,” a play on the usual “open skies” terminology for aviation treaties.

The deal opens Tokyo’s close-in Haneda Airport to more U.S. flights during daytime hours. Delta, which operates mostly at Narita Airport an hour east of Tokyo, fears rivals American and United gain more access to Haneda because they have joint ventures with Japanese airlines. Delta does not.

Delta has argued the deal tips the competitive balance and could make its Narita flights unviable. It also operates a small connecting hub at Narita. The airline had launched a PR and lobbying effort in recent weeks to try to stop the deal.

“Delta is committed to doing our best to maintain the viability of our current Asian route structure and our Narita hub for as long as possible, recognizing that commercial impacts are imminent,” the Atlanta-based airline’s chief legal officer, Peter Carter, said in a statement Thursday.

“Delta will make a careful assessment and adjust our network accordingly,” he added.

Although Delta is concerned that the deal could cause its Narita hub to unravel, “whether that happens, who knows?” said Brett Snyder, a former airline manager who runs a consumer airline blog at crankyflier.com.

Snyder was doubtful, though, that the deal will scuttle Atlanta-Tokyo flights.

“This is a big route between two major world business centers,” Snyder said. “If you’re the only game in town between Atlanta and Tokyo, you’re probably still going to be flying.”

Snyder said Delta’s problem was that its position “happens to be against the interest of all the other airlines,” Snyder said.

Delta was arguing against gradual liberalization, while in U.S. aviation policy, “all trends have been toward liberalization,” he added.

United and American both welcomed the deal in statements Thursday morning, saying it will benefit customers to have convenient access into the heart of Tokyo.

The deal opens five daytime slots for trans-Pacific operations at Haneda airport for U.S. carriers and five for Japanese carriers – in addition to one new nighttime slot each, according to Delta. Delta expects to get at least one daytime slot.

Industry group Airlines for America, which Delta left last year over differences on policy matters, applauded the deal.

“Enabling all U.S. carriers to compete for access at Haneda – one of the world’s largest and busiest airports – helps to improve international relations with our Japanese partners, while yielding immense benefits for the traveling and shipping public,” said Nicholas Calio, CEO of the trade group.