The harassment of Dr. Cerón and her colleagues was never proven to be carried out by the industry, and federal prosecutors declined to investigate. In response to questions from The New York Times, Coke and Pepsi said they were not involved, and Postobón, the soda company that filed the complaint about the organization’s ad, deferred comment to The National Business Association of Colombia. The association, which represented national and international beverage makers on the soda tax issue, said it had nothing to do with the episodes.

The International Council of Beverages Associations, the parent organization of trade groups around the world fighting the taxes, would not directly answer the question about whether its allies in Colombia were connected to the alleged harassment, but it condemned such actions.

“We reject under any circumstance the improper influence or harassment of any individual or organization for any purpose, at any time, in any way,” Katherine W. Loatman, executive director of the organization, said in a statement.

The experience in Colombia may be the most extreme, but a juggernaut of industry opposition has killed or stalled soda tax proposals around the globe, including in Russia, Germany, Israel and New Zealand.

Nevertheless, the idea is gaining momentum; such levies have been enacted in 30 countries, including India, Saudi Arabia, South Africa, Thailand, Britain and Brunei. More than a billion people now live in places where such taxes have driven up the price of sugar-sweetened beverages.

The battles have been particularly intense in emerging markets as the industry seeks to make up for falling soda consumption in wealthier nations. Latin America has surpassed the United States as the world’s biggest soft-drink market, according to the World Health Organization, with sales of carbonated soft drinks doubling there since 2000 while they declined in the United States.

The beverage industry asserts that soda taxes unfairly burden the poor, cause higher unemployment by squeezing industry sales, and fail to achieve their policy goal: reducing obesity. Studies of soda taxes have shown they lead to a drop in sales of sugar-sweetened beverages — a 10 percent sales decline, for example, over the first two years of Mexico’s tax — however, such measures are so new that there is not yet evidence of their impact on health.