Alaska Airlines and Hawaiian Airlines can move forward with their planned $1.9 billion merger, the United States Department of Transportation (DOT) said in a press release on Tuesday.

However, the two carriers are required to maintain the value of their airline reward systems and preserve existing service on key Hawaiian routes to the continental United States and inter-island.

"Our top priority is protecting the traveling public’s interest in this merger. We have secured binding protections that maintain critical flight services for communities, ensure smaller airlines can access the Honolulu hub airport, lower costs for families and service members, and preserve the value of rewards miles against devaluation," Transportation Secretary Pete Buttigieg commented.