From Politico:

“We (Sens. Rand Paul, Ted Cruz and Mike Lee) will oppose the motion to proceed to any legislation that will serve as a vehicle for any additional gun restrictions,” the three conservatives wrote in a copy of the signed letter obtained by POLITICO.

White House responds in predictable fashion:

“A vote ought to be held on all these elements,” said White House press secretary Jay Carney. “It is what the victims of gun violence deserve. I don’t think you could tell the families of those who have lost their children to gun violence — that bills like this might be filibustered.”