Sens. Rand Paul, R-Ky., Mike Lee, R-Utah, and Ted Cruz, R-Texas, wrote a three paragraph letter to Senate Majority Leader Harry Reed saying they will filibuster any new gun restrictions.
"The Second Amendment to the Constitution protects citizens' right to self-defense. It speaks to history's lesson that government cannot be in all places at all times, and history's warning about the oppression of a government that tries," they wrote.
The pledged to "oppose the motion to proceed to any legislation that will serve as a vehicle for any additional gun restrictions," The Hill said Tuesday.
The Obama administration had initially hoped to include an assault weapons ban in the gun legislation by Reed dropped it from the bill, acknowledging it doesn't have the support to pass the Senate.
The legislation proposes universal background checks and limits the number of bullets that can be held by a single clip of ammunition, among other changes.