A U.S. federal court on Tuesday heard a debate whether the National Security Agency (NSA)'s collection of Americans' phone records is legal and constitutional.

An American Civil Liberties Union (ACLU) lawyer went into an argument with the lawyer defending the government's bulk collection of telephone records regarding the violation of Americans' privacy.

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The debate centered on  whether the NSA's conduct violated the Section 215 of the Patriot Act as well as the Fourth Amendment.

The NSA's move was part of the agency's counter-terrorism program following 9/11 attacks. 

The program was revealed in July 2013, when former NSA contractor Edward Snowden leaked confidential NSA documents. Shortly after the program was publicized, the ACLU challenged its legality and constitutionality.

The NSA program entails the mass collection of Americans' phone records from telephone companies, the information gathered includes the numbers dialed, length and time of conversation. The agency reportedly used the information to analyze whether the calls were made to terrorists abroad.

In defense, the government gave its controversial interpretation of Patriots Act's Section 215.

The statute stipulates that records "must be relevant" to government authorized investigations, but it was only until last year that it was revealed that the "relevance" included obtaining call records from phone companies.

The debate lasted for about two hours and among the points of discussion was whether the Congress had knowledge of the program when the statute was made.

ACLU staff attorney Alex Abdo told the judges that the NSA's conduct can be the precedent for future government programs that violates the rights of innocent Americans.

Stuart Delery, assistant attorney general of the Justice Department's Civil Division, countered that the Congress knew about the program when the statute was re-authorized in 2010 and 2011.

Delery said the government needed to collect the phone information to "detect and disrupt" terror plots before an attack occurs.

TagsNSA, federal courts, phone records