Tempers are flaring in the Senate.

With lawmakers slated to take procedural votes later this evening on a bill to reform the PATRIOT Act, Sens. Dan Coats (R-Ind.) and John McCain (R-Ariz.) refused to yield the floor to fellow Republican Sen. Rand Paul, who has promised to force a sunset of key parts national security law. The spat prompted a terse back-and-forth during a rare Sunday session prompted by Paul's refusal earlier this month to allow votes on the issue.

With dozens of Senate onlookers donning "Stand with Rand" T-Shirts, Paul tried to interject as Coats and McCain were speaking in defense of of the National Security Agency. But McCain and Coats wouldn't yield the floor.

Paul "needs to learn the rules of the Senate," McCain sniped at the Kentucky Republican.