Mayor Michael Bloomberg and Weight Watchers North America President David Burwick announced the groups join a list of physicians, elected officials and others who have come out in support of the plan.
"There has been a lot of discussion about obesity, but little action, which is why we at Weight Watchers support what this administration is doing to help New Yorkers live healthier," Burwick said. Along with his organization and Jenny Craig, the creator of the South Beach Diet, the founder of The Best Life and other diet experts expressed their support.
Opponents, too, are counting their ranks: An opposition group called New Yorkers for Beverage Choices said Friday it has the backing of more than 2,000 businesses and 201,000 individuals. Some City Council members have criticized the plan, which isn't scheduled to come before them for a vote.
The proposal is set to go to a Sept. 13 vote at the city Board of Health. Its members are appointed by Bloomberg.
The proposal call for restaurants, movie theaters, sports arenas, food carts and delis to stop selling sodas and other sugary drinks in servings larger than 16 ounces.
Bloomberg says the proposal is a sensible way to fight obesity in a city that spends billions of dollars a year on weight-related health problems.
"Our proposal for reasonable portion sizes won't prevent anyone from buying or drinking as much soda as they want," he said Tuesday, noting that people could choose to buy more than one cup or bottle.
"But it will help people keep from inadvertently taking in junk calories" just because a beverage is jumbo-sized, the mayor said.
Opponents say the city is overstepping its authority and infringing on personal freedom.
"New Yorkers are smart enough to decide for themselves what to eat and drink," said Eliot Hoff, a spokesman for New Yorkers for Beverage Choices.
New York City also bars artificial trans fats from food served in restaurants.