WASHINGTON (Reuters) – The U.S. Transportation Department said on Tuesday it had agreed to allow Alaska Airlines to close on its $1.9 billion acquisition of Hawaiian Airlines, after the carriers agreed to maintain key Hawaiian routes and adopt consumer protections.

The Justice Department in August opted not to block the deal that was announced in December by Alaska, the fifth-largest domestic U.S. airline, to Hawaiian, the 10th-largest carrier.

DOT said Alaska and Hawaiian agreed to protect the value of frequent flyer rewards, maintain existing service on key Hawaiian routes to the continental United States and inter-island, ensure competitive access at the Honolulu airport and provide travel credits or frequent flyer miles for disruptions that are the fault of the airline.

(Reporting by David Shepardson; Editing by Mark Porter)