NEW YORK (Reuters) - A federal appeals court on Monday allowed rights groups to challenge a spy law that allows U.S. intelligence agencies to eavesdrop on foreign communications without court approval.

The 2nd Circuit Court of Appeals in New York overturned a lower court ruling and granted rights groups the legal ground to challenge a 2008 amendment to the Foreign Intelligence Surveillance Act, or FISA.

At the time of the 2008 bill, critics complained it allowed warrantless surveillance of the phone calls and e-mails of Americans who communicate with foreign targets.

The American Civil Liberties Union and others sued the U.S. attorney general and other government officials in July 2008.

They argued they had the standing to fight the law because they suspected their communications with people abroad were being monitored. The court ruled that costly steps taken to avoid being monitored represented evidence of fear.

"We therefore find that plaintiffs have standing to challenge the constitutionality of the (amendment) in federal court," the 63-page opinion said.

The appeals court opinion did not directly address the merits of the suit's claims.

(Reporting by Basil Katz; Editing by Daniel Trotta)