The U.S. Justice Department is preparing to file a lawsuit challenging American Airlines Group Inc's partnership with JetBlue Airways Corp on antitrust grounds, the Wall Street Journal reported on Tuesday, citing people familiar with the matter.

The lawsuit could come as early as Tuesday, the newspaper said.

The airlines' "Northeast Alliance" partnership was announced in July 2020 and approved by the U.S. Transportation Department six months later, shortly before the end of the Trump administration.

The codeshare agreement allows American and JetBlue to sell each other's flights in their New York-area and Boston networks and link frequent flyer programs, in a move aimed at giving them more muscle to compete with United Airlines and Delta Air Lines in the U.S. Northeast.

(Reporting by Diane Bartz and David Shepardson in Washington, Abhijith Ganapavaram in Bengaluru; Editing by Ramakrishnan M. and Paul Simao) ((Abhijith.G@thomsonreuters.com;))