American Airlines Group Inc. said its unit U.S. Airways Group merged with the company, as part of efforts to integrate operations of the businesses following a merger in 2013.

American Airlines Group, the owner of American Airlines, said U.S. Airways Group and its airline U.S. Airways ceased to exist as a separate entity effective Dec. 30, 2015.

The companies have already been using a single booking system and operating as a single brand since October. 

The change is merely an administrative step and does not affect the company's employees or customers, American Airlines spokesman Matt Miller told Reuters.

"With US Airways merged into American Airlines and U.S. Airways Group merged into American Airlines Group, all of their obligations (including debts and liabilities) become the obligations of American Airlines and American Airlines Group, respectively," Miller said.

American's shares were down about 2 percent at $42.00 in morning trading on Thursday.

(Reporting by Ankit Ajmera in Bengaluru; Editing by Shounak Dasgupta)