(Newser) – If Harry Reid goes forward with a possible gun-control measure, he'll face a filibuster, say three Republican senators. Rand Paul, Ted Cruz, and Mike Lee have penned a letter to the Senate majority leader, saying, "We will oppose the motion to proceed to any legislation that will serve as a vehicle for any additional gun restrictions." They don't actually use the word "filibuster," Politico notes, but their meaning is clear. The bill would expand background checks and toughen rules on interstate gun trafficking; it could also contain amendments limiting magazine capacity and some assault weapons, though those measures wouldn't pass, Politico adds. (Read more filibuster stories.)