By Evan Perez
CNN Justice Reporter
(CNN) -- The Justice Department on Friday appealed a December federal court decision threatening the National Security Agency's program that collects data on nearly every phone call made in the United States.
The ruling by U.S. District Judge Richard Leon in Washington found the program was likely unconstitutional.
Another federal judge in New York has since ruled in a separate case the program is lawful.
The American Civil Liberties Union, which brought that lawsuit, is appealing the ruling.
Split decisions likely set the stage for legal wrangling over the course of the coming year that could ultimately result in a Supreme Court case.
Details of bulk NSA surveillance of electronic data were revealed last year in leaks by former agency contractor Edward Snowden.
CNN's Bill Mears contributed to this report.
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