(CNN) - A trio of Republican senators say they will block any gun control legislation that they consider a threat to Second Amendment rights.

Republican Sens. Rand Paul of Kentucky, Mike Lee of Utah and Ted Cruz of Texas plan to oppose a bill that "would infringe on the American people's constitutional right to bear arms, or on their ability to exercise this right without being subjected to government surveillance."

Their comments came in a letter obtained by CNN and addressed to Senate Majority Leader Harry Reid, dated March 22. The letter, first reported by Politico, is expected to be delivered on Tuesday.

Reid formally introduced legislation on Thursday that calls for an expanded background check system and tougher laws on gun trafficking. In addition, he'll permit amendments to the bill, so senators can vote on a ban against semiautomatic firearms modeled after military-style weapons and a proposal to limit magazine capacities. Both proposals have support from liberal Democrats.

The Senate will debate the bill when the chamber returns in April after a two week recess.

Whether or not the three senators' opposition comes in the form of Paul's high profile talking filibuster earlier this month is unclear, but both Cruz and Lee were instrumental in helping the Kentucky senator carry on the near-13 hour stand-off.

Paul, Cruz and Lee--all first term senators elected with strong tea party support--cited fears of government oppression in their letter, saying the Second Amendment protects citizens' right to self-defense and speaks to "history's lesson that government cannot be in all places at all times."

Proponents of the proposed gun legislation say the new bill does not interfere with the Second Amendment. New York City Mayor Michael Bloomberg, a leading voice in the gun control push, argues the legislative agenda is not about trying to get rid of guns, but about the public "wanting to be safe on their streets."

"This is about the public having the right to buy arms and the right to protect themselves and the right to use them for sport or hunting," Bloomberg said Sunday on NBC. "But also, it's about the public's right to keep guns out of the hands of criminals and the mentally ill. That's in everybody's interests.

The senators' three-paragraph letter doesn't mention the word filibuster but appears to be a clear warning that the conservative firebrands will vehemently stand against any "vehicle for any additional gun restrictions."