The plan would have forced people buying guns over the Internet and at gun shows to undergo a background check. It needed 60 votes to pass the Senate, but only received 54.
"You're either in favor of continuing the killing and the tragedies or you're not. This was an up or down vote," he said.
President Obama as well as a vast majority of Americans had given the bill an up vote. Bloomberg says the outcome is not good news for the Senators who voted against it.
"You wait until the next November when people run against them and they say look at how many more people died since they voted to stop sensible rules that would simply keep the guns out of the hands of criminals and the mentally," Bloomberg argued.
Those Senators who voted against the legislation say they agree that the system has to be changed, but they say this effort goes too far.
"This is a slippery slope of compromising the Second Amendment and you go down that road you're going to find it easier to compromise other things in the bill of rights," Republican Senator Chuck Grassley said.
"It would lay the groundwork for even more draconian and ineffective gun control measures," Republican Senator Richard Shelby said.
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."
Bloomberg has attributed New York City's falling violent crime numbers in recent decades to the city's restrictive gun laws. The National Rifle Association has argued that tighter laws would have no effect on public safety and crime.