“I was stunned during the break when I got a letter from 13 Republican senators,” Reid said on the Senate floor Tuesday. “They’re the ones who complain the most about not having regular order around here … [but] they said they don’t think there should be a discussion, a debate on guns.

“How would I describe these 13 senators? It’s hard because I want to be respectful … but they’re speaking out of both sides of their mouth.”

Reid filed a motion to proceed on S.649, the Safe Communities, Safe Schools Act.

The Senate gun reform bill would expand background checks on gun purchases, create new penalties on straw purchases and include new funding for school security. The bill doesn’t include an assault weapons ban or limits on magazine clip capacity — although Reid promised to allow a vote on those provisions as an amendment.

Republicans have expressed concern that extending background checks could create a federal registry of gun owners and make it harder for family members to transfer firearms. Sen. Chuck GrassleyCharles (Chuck) Ernest GrassleyFBI informant gathered years of evidence on Russian push for US nuclear fuel deals, including Uranium One, memos show Klobuchar taking over Franken's sexual assault bill Lawyer: Kushner is 'the hero' in campaign emails regarding Russia MORE (R-Iowa) is also crafting his own gun violence bill as an alternative to the Democratic proposal.

Reid said the Senate owes it to the victims of the Newtown, Conn., shooting where 20 first-graders and six school employees were killed by a gunman in December.

The Senate is expected to begin debate this week on the gun-control reform package.

President Obama has launched a public effort to rally support for gun control, visiting states that have enacted tougher laws in the aftermath of shootings and speaking with families of victims of gun violence.