The airlines said the Justice Department had declined to challenge the merger in court.

Alaska Airlines’s acquisition of Hawaiian Airlines cleared a major hurdle on Monday, after the airlines said the Justice Department ended a review of the merger without challenging it on antitrust grounds.

The approximately $1.9 billion deal, the first major U.S. airline merger in nearly a decade, is set to expand Alaska’s operation and solidify its position as the country’s fifth-largest airline. The combined company would still be small relative to the four large airlines that dominate U.S. air travel, commanding roughly half the market share of United Airlines.

The airlines said they would wait to proceed with the merger until receiving final approval from the Department of Transportation.

Gov. Josh Green of Hawaii, which relies heavily on Hawaiian Airlines, praised the deal and thanked the Justice Department for taking the state’s needs into account in its review.

“I am confident that

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