June 30 (Reuters) - The U.S. Supreme Court rejected on

Monday a request by American Airlines ( AAL ) to overturn a

judicial decision that found that the company's now-scrapped

U.S. Northeast partnership with JetBlue Airways ( JBLU )

violated federal antitrust law.

The justices turned away an appeal by American Airlines ( AAL ) of a

lower court's decision in a lawsuit brought by the U.S. Justice

Department that led to the end of the proposed "Northeast

Alliance," which would have allowed the two carriers to

coordinate flights and pool revenue.

The American Airlines ( AAL ) argued that the antitrust violation

ruling by the Boston-based 1st U.S. Circuit Court of Appeals

wrongly embraced a hostility to collaboration between businesses

and was contrary to the approach taken by other courts to

require evidence of actual harm to consumers in the market as a

whole, not just the customers of the collaborators.

The company also said the ruling invalidated a joint venture

that increased market-wide competition among all airlines and

"threatens to wreak havoc on productive collaborations of all

shapes and sizes."

The November ruling came in a lawsuit the Justice Department

filed in 2021 along with six states during Democratic President

Joe Biden's administration. Under Biden, the Justice Department

made boosting airline competition a top priority and

aggressively enforced U.S. antitrust laws.

Despite a change in administrations, the Justice Department

under Republican President Donald Trump has continued to defend

the government's victory in the American Airlines-JetBlue case,

saying the 1st Circuit's ruling upholding a judge's decision

blocking the alliance rested on "uncontroversial antitrust

principles."

The alliance was announced in July 2020 and approved by the

U.S. Transportation Department just days before the end of

Trump's first administration in January 2021.

Through their partnership, American, the nation's largest

airline, and JetBlue ( JBLU ), the sixth-largest, joined forces for

flights in and out of New York City and Boston, coordinating

schedules and pooling revenue.

The Justice Department argued that the alliance would hurt

consumers by eliminating incentives for American to cut prices

to lure customers from JetBlue ( JBLU ), a historically disruptive rival

with often lower fares.

U.S. District Judge Leo Sorokin in Boston in 2023 sided with

the Justice Department and found the alliance violated antitrust

law.

Following Sorokin's ruling, JetBlue ( JBLU ) terminated the alliance,

as it unsuccessfully sought to bolster its efforts to win

approval for the now-dropped $3.8-billion purchase of Spirit

Airlines, which Biden's Justice Department also

successfully challenged.

American Airlines ( AAL ), though, pressed ahead with an appeal,

saying the ruling would prevent the company from entering into

any similar future arrangement, including with JetBlue ( JBLU ). But a

three-judge 1st Circuit panel upheld Sorokin's decision.