The theory behind the proposed ban is that smokers subject more people to passive smoke if they walk.
Mr Koo said: "This bill is not against smoking, just don't do both together."
The city has already banned smoking in most restaurants and bars, offices, and public venues including parks.
Ceia Cremo, 48, who was smoking as she walked down Fifth Avenue, told the New York Daily News: "I think it's unreasonable. Where else do I have left to smoke? You can't smoke in the park, you can't smoke in a lot of places."
Another New York smoker told Fox5: "I'm not standing in one spot. It's not gonna happen.
"As I'm walking, it's outside, I'm not blowing it in anyone's faces."
Others opposed to the plan argued it could unnecessarily take up policing resources as officers fine walking smokers.
Mr Koo told the New York Daily News: "In a perfect world every smoker would have the self awareness to realise smoking while walking subjects everyone behind you to the fumes.
"It has happened to me many times. I'm walking behind someone who's smoking, and I'm suffering for five or 10 minutes.
"I see mothers with their strollers walking behind people who smoke, and they're exposing the baby to secondhand smoke."
Last year Bill de Blasio, New York's mayor, signed a law to increase prices and taxes for tobacco related products.