Sen. Rand Paul (R-KY) earlier this week revealed that another senator had told him that he was surveilled by the Obama administration.

“I know one other senator who’s already confided to me that he was surveilled by the Obama administration, including his phone calls,” he told Fox News on Friday.

“So when this all comes out, if there are political figures from the opposition party, it’s a story bigger than any of the allegations with regard to Russian collusion,” he said.

Earlier this month, Paul announced that sources have told him that he has been surveilled by the Obama administration, and that he has requested information from the White House and the congressional intelligence committees on whether he has ever been surveilled, unmasked, or searched for in intelligence reports.

“It’s about your own government spying on the opposition party, that would be enormous if true,” he said. “I don’t know the truth. We’ve asked the intel committees, House and Senate, and I’ve also asked the White House, because there is this whole discussion of Susan Rice unmasking people,” he said.

Former National Security Adviser Michael Flynn was fired in February, after a phone call he had with Russian Ambassador Sergei Kislyak was leaked to the Washington Post.

Listening in on an American’s phone calls is illegal without a warrant, but it can happen legally during surveillance of a foreign target. If Americans are caught up in surveillance of a foreign target, their identities are supposed to be “masked,” or concealed.

However, U.S. officials can request to have their names unmasked if it is necessary to understanding the context of the communications, with the approval of the agency conducting the surveillance.

Former Director of National Intelligence James Clapper revealed that last year, 1,934 Americans’ names were unmasked.

Last month it was reported that Susan Rice had unmasked Trump campaign officials — which she has not denied, but only claimed that it was not illegal.

“There was no reason for her to unmask people. Hers was not a position of investigation. Hers was a political position. And for her to get involved with unmasking Trump officials is alarming. If it happened to other people, it’s even more alarming,” he said.

“But we’re going to try to get to the bottom of this. And it’s a very secret world. You have to realize that it’s a world so secret most members of Congress are never allowed.”