While Paul's Facebook page and political action committee website didn't say how many people had signed up to become part of his litigation, the Lexington (Ky.) Herald-Leader reported more than 250,000 people had done so by Saturday afternoon.
His RAND PAC site says the senator is seeking 10 million people to join up. Providing unverified information sought on sign-up links on Paul's Facebook page and PAC website takes the user to a page on his Rand for Senate 2016 website requesting donations to help spread the word about his yet-to-be-filed suit.
Paul, a Tea Party-backed critic of NSA eavesdropping and data collection on millions of Americans, said the lawsuit would be aimed at protecting the Fourth Amendment's prohibition against unwarranted searches.
"The question here is whether or not, constitutionally, you can have a single warrant apply to millions of people," Paul said on Fox News Friday. "So we thought, what better way to illustrate the point than having hundreds of thousands of Americans sign up for a class action suit."
He said the measure is "kind of an unusual class-action suit" because any American with a cellphone is eligible to join. Paul said hundreds of thousands of supporters have said they would sign onto the measure.
The Kentucky conservative has found an unlikely ally in his opposition to the NSA in Sen. Bernie Sanders, Ind-Vt., a liberal who caucuses with Democrats.
Sanders has been a harsh NSA critic on Capitol Hill, MSNBC reported Friday. The same day Paul announced his plans for a lawsuit, Sanders sent the NSA director a letter questioning whether the agency had ever spied on members of Congress.
Both senators have introduced legislation that would sharply curtail the NSA's ability to collect phone and other electronic data on millions of unsuspecting Americans -- the vast majority of whom are not suspected of any wrongdoing and who have no links to terrorists.
The news comes on the same day the secretive court assigned to oversee NSA data gathering extended the program's warrant for another 90 days, Fox said. The extension comes after conflicting federal court rulings, one that called the program illegal and another that said it is within in federal government's powers to collect the data in the interest of public safety.