Alaska Airlines and Hawaiian Airlines just took one step closer to a merger, according to statements sent out on Monday.

The deal cleared a regulatory obstacle when "the time period for the U.S. Department of Justice to complete its regulatory investigation of the proposed combination of Alaska Airlines and Hawaiian Airlines under the HSR Act" expired, Alaska Airlines said in a statement on its website. 

The announcement boosted shares of Hawaiian by nearly 9% in premarket trade on Tuesday, while Alaska's shares were flat. The merger is a $1.9 billion deal. 

"Over the past several months, my administration and I have worked with the leadership of Alaska Airlines to carefully review the potential impacts of a consolidation and we insisted that any changes expand travel options for our residents and preserve union jobs," Hawaii Gov. Josh Green said in a press release. 

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The proposed airline combination is now subject to approval from the U.S. Department of Transportation.

"Following that step, we will complete work to close the transaction, and proceed with integrating the two companies, welcoming Hawaiian Airlines guests and employees into Alaska Air Group, and expanding benefits and choice for consumers throughout Hawai‘i, the Asia-Pacific region, continental United States and globally," Alaska Airlines said. 

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Green said Alaska Airlines plans to maintain the Hawaiian Airlines brand, and "reinforced commitments" to preserve and grow union jobs in the Aloha State. He believes the merger would "expand the number of destinations throughout North America for Hawai‘i residents that can be reached nonstop or one-stop from the islands."

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Mergers and acquisitions in the aviation industry have faced tough scrutiny from regulators. Earlier this year, a federal judge blocked JetBlue Airways' planned $3.8 billion acquisition of ultra-low-cost carrier Spirit Airlines.

Reuters contributed to this report.