Friday marks six months since the shooting in Newtown, Connecticut and the mayor's gun reform lobby will commemorate the day with a new campaign.
Mayors Against Illegal Guns will begin a bus tour to try to persuade lawmakers to reconsider the background check bill that was voted down in the Senate this spring.
The first stop on the tour will be Newtown, where the daughter of the principal of Sandy Hook Elementary will join the group.
For more information about where the campaign will stop, visit demandaction.org.
Meanwhile, Bloomberg is asking campaign donors to close their wallets to Democratic legislators who oppose gun control.
The mayor is referring to Sens. Max Baucus, Mark Begich, Heidi Heitkamp and Mark Pryor.
He said the senators voted against gun sale background checks in April, an act Bloomberg called "a slap in the face to Americans everywhere."
"This is something that I feel very strongly about," Bloomberg said on MSNBC's "Morning Joe." "Twelve-thousand Americans get killed every year from illegal handguns. Nineteen-thousand kill themselves with illegal handguns. Background checks work. There's plenty of evidence of that. And we're dealing right now with this particular election."
Bloomberg called out the four lawmakers in a letter to 1,100 New York donors.