The Senate bill to expand background checks for gun buyers drew 54 votes Wednesday, six short of the 60 needed to advance.
The measure was among those defeated despite lobbying by former U.S. Rep. Gabby Giffords, wounded in a shooting at an event in her Arizona district, and by family members of those killed by Adam Lanza in Newtown, Conn., in December.
Bloomberg, a billionaire media mogul, said he would work to defeat senators who voted against the background checks and urged other New Yorkers to do the same.
"I've said before, I will support those who do what's right for America," Bloomberg said. "I'm going to support those who did the right thing. And if there's an election between somebody who didn't and somebody who wants to, of course I'm going to do that, and I would hope you would do that, too."
Speaking at a Manhattan news conference to promote energy-saving initiatives, Bloomberg lashed out at gun control opponents.
"This just is over the top," he said. "When 80 or 90 percent of the people want to do something, when the issue is simply do you continue murder or not, do you continue this terrible suicide rate among people who have problems or not . . . it's so inconceivable to me that some of these senators voted the way they did. How can you look at constituents in the eye when you go home?"
Bloomberg has attributed New York City's falling violent crime numbers in recent decades to its restrictive gun laws. The National Rifle Association has argued that tighter laws would have no effect on public safety and crime.
The NRA did not immediately return a call Thursday seeking a comment on Bloomberg's vow to go after senators who voted against the gun law.