(Reuters) - Alaska Air ( ALK ) said on Thursday it has agreed to further extend the review period of its proposed $1.9 billion acquisition of peer Hawaiian Holdings ( HA ) with the U.S. Department of Justice (DOJ).

The companies will extend the review period with the DOJ until 12:01 AM ET, Aug 20.

On Wednesday, the airlines had said the review period was extended until 12:01 AM ET on Friday.

The deal was announced last year and the carriers said in March they "have been working cooperatively with the DOJ and expect to continue to do so".

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.