A protester wearing a Guy Fawkes mask holds a mock TV camera during a demonstration against the National Security Agency. Reuters

The U.S. Supreme Court could soon be asked to decide the constitutionality of the federal government's massive data collection of phone records after two lawsuits challenging the National Security Agency's controversial surveillance program have begun to inch forward in federal circuit court for the first time. The American Civil Liberties Union and other privacy rights groups have denounced the NSA's data collection program, first revealed by former contractor Edward Snowden last summer.

"The phone-records program – under which the NSA collects a record of the calls made by millions of Americans every single day – is perhaps the most sweeping surveillance operation ever directed against the American public by our government," Alex Abdo, an ACLU staff attorney, said in a statement Tuesday. "It raises profound questions about the role of government in a democracy and about the future of privacy in the digital era. And it threatens our constitutional rights in ways unimaginable by the founders of our country."

The NSA stores information about calls received and made on major U.S. telephone networks, including the time and length of the calls. The government claims it uses the information to track terrorist suspects.

ACLU lawyers called the surveillance program unconstitutional Tuesday in an oral argument before the Second U.S. Circuit Court of Appeals in New York. The DC Circuit Court is set to hear arguments in a similar case on Nov. 4. The surveillance program has previously been debated in district courts. An appeal in either circuit court case could come before the Supreme Court.

The U.S. government argued in court papers that the ACLU and other groups suing over the data collection program lack legal standing because they can’t show their telephone data was reviewed by the NSA. The ACLU lawsuit was filed in June 2013, days after Snowden disclosed the program.

Members in both houses of Congress have proposed laws to overhaul the data collection program, but they are unlikely to be acted on this year, said the Wall Street Journal.