The campaign, called New Yorkers for Beverage Choices, calls out the proposed ban over restricting freedom, as opposed to promoting healthier drink choices, The New York Times reported.
On Thursday, the group aired its first radio ad attacking the proposal.
"This is New York City; no one tells us what neighborhood to live in or what team to root for," says the narrator of the ad. "So are we going to let our mayor tell us what size beverage to buy? It's unbelievable!"
New York City has spent $2.8 million on its own campaign to influence public opinion since 2009, which has included subway, print, online and television ads linking soft drink consumption to obesity.
The ban only needs to be approved by the New York City Health Board, whose members were appointed by Mayor Michael Bloomberg. The board is holding a public hearing on the proposal on July 24.
"There's an impartial group of health experts who are going to make the decision," said Howard Wolfson, a deputy mayor who is overseeing the proposed ban. "I think they will be influenced by science and not any PR campaign."