A federal appeals court is hearing arguments today in a lawsuit over the NSA's massive program of collecting data from phones.

Under the controversial program, the NSA collects metadata such as frequency of phone calls, the numbers dialed and even the length of conversations.

NSA supporters call it an effective way to fight terrorism, but privacy advocates say this spying on Americans is illegal government overreach.

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Judge Andrew Napolitano explained on "Fox and Friends" that the key issue is whether or not the NSA's general warrant that it obtained from a secret court is legal and validates the invasion of privacy.

Three federal judges have ruled on this, with two saying it's legal. But one judge disagreed, stating the government must find a better and more constitutional way to protect American citizens.

Ultimately, Judge Nap said, this will make its way to the Supreme Court, because when judges and appellate courts differ, that means the Constitution means different things in different parts of the country, which is obviously not good.

Watch the clip above.