Efforts to protect the only nonstop flight between Minnesota and Asia suffered a severe setback Thursday, as the United States and Japan agreed on a deal that Delta Air Lines has warned could imperil its Minneapolis-Tokyo service.

The agreement provides for more daytime landing slots for trans-Pacific flights at Tokyo’s Haneda Airport, according to a release from the U.S. Embassy in Japan. Delta flies to Narita International Airport, 46 miles from downtown, and executives have said the new plan favors rivals American and United airlines.

Elected officials from Minnesota have argued vigorously to save the Tokyo route, which was started by Northwest Orient in 1947 and was the nation’s first commercial air service to Japan. U.S. Sen. Amy Klobuchar, Rep. Betty McCollum and Gov. Mark Dayton complained about the decision personally to Vice President Joe Biden before he appeared at a Thursday ceremony in St. Paul.

“He heard it loud and clear from the delegation,” McCollum told the Star Tribune.

Klobuchar, Dayton and Sen. Al Franken met personally with U.S. Transportation Secretary Anthony Foxx two weeks ago, a meeting that gave rise to a two-week delay in negotiations.

Nonetheless, aviation officials moved ahead with a plan that is likely to shift traffic to Haneda, where American and United are the strongest U.S. carriers.

The pact gives U.S.-based airlines five daytime slot pairs — arrivals and departures — between 6 a.m. and 11 p.m., and one nighttime slot pair.

The previous arrangement allowed U.S. carriers only four slot pairs, all during the overnight hours.

Atlanta-based Delta — the dominant carrier at Minneapolis-St. Paul International Airport — picked up the Tokyo route along with a hub at Narita in its 2009 acquisition of Northwest Airlines. The airline said it is “deeply disappointed with the final agreement,” which it believes favors its rivals to such a degree that Delta’s Asia network could unspool.

“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,” Delta’s executive vice president and chief legal officer, Peter Carter, said in a statement. “Delta will make a careful assessment and adjust our network accordingly.”

Narita became Tokyo’s international hub in 1978, though a new runway at Haneda and other improvements have gradually shifted some international traffic in recent years.

But until Thursday, the U.S.-Japan Open Skies Agreement did not allow for daytime flights for U.S. carriers.

The expansion benefits Delta’s rivals chiefly because they have partnerships with Japan’s two major airlines. Delta’s effort to develop a partnership with a smaller Japanese airline hasn’t succeeded.

While Delta is eligible to apply for the slots, it says it will likely only be granted one or two.

Without a Japanese partner airline to transfer its passengers on to other points throughout Asia, it would struggle to make a couple of routes into Haneda profitable.

At this point, Delta is not expected to receive a gate or slot at Haneda, said Jeff Hamiel, executive director and chief executive of the Metropolitan Airports Commission.

“MSP-to-Tokyo is very, very important to us. Many business travelers fly it regularly. We don’t want to lose a service we have had for over 70 years,” Hamiel said. “We are going to explore some additional options to see if we can’t apply some pressure to the Japanese government, but to be honest we’ve explored nearly every option at this point.”

Delta anticipates losing many of its Tokyo passengers from New York and Los Angeles to other carriers.

Nonstop international flights from its other hub cities, like Detroit and Minneapolis, need feeder passengers from other markets to fill aircraft.

These passengers will eventually choose a flight on a different airline if it means they can get into downtown Tokyo more quickly. As a result, Delta says, Tokyo could eventually prove unprofitable.

The U.S. government, which faced fierce opposition from Delta and Minnesota’s congressional delegation, contends “several U.S. carriers have expressed strong interest in offering daytime service to Haneda, and their passengers will benefit from convenient access to downtown Tokyo,” according to the Embassy news release.