The law banning smoking in bars and restaurants came into effect two weeks ago at the behest of the mayor, Michael Bloomberg.

Dana Blake, 32, a bouncer in the Guernica bar in the East Village, approached Jonathan and Ching Chan in a crowded basement early on Sunday morning and asked for the cigarette to be put out.

When Jonathan Chan began to argue, Blake grabbed him by his neck and dragged him towards the exit; to throw him out, the police said.

Jonathan fought back and his brother and two others joined in. As the fighting spilled into the street, Blake was stabbed in the abdomen.

Travis Keyes, the owner of the next door bar, said: "It's so ironic: something that's supposed to save lives has already taken a life."

Blake's brother Anthony said: "The common person always plays victim of these political laws ... I want to know if it was worth one person's life for that cigarette."

The brothers have been charged with assault, criminal possession of a weapon and resisting arrest while the police try to discover who stabbed Blake.

The New York authorities say they will not enforce the ban rigorously until the beginning of next month. Bar owners say business has fallen off in the past fortnight.