The Children's Food Campaign (CFC) has asked the Food and Drink Federation (FDF) to stop opposing the tax on sugary drinks, claiming its top UK member brands are less aggressively opposed to the duty than the trade association.
Out of 55 FDF members contacted by CFC, 14 gave full responses, including Birdseye, Slimfast, Wrigleys, Mars, Weetabix and Haribo.
Seven companies had no formal position on the tax, four explicitly backed the FDF and three gave other responses.
CFC's criteria for selection said the company had to be a recognisable brand and a manufacturer of food rather than primarily soft drinks, tea or coffee.
Malcolm Clark, CFC coordinator said the campaign would have liked to go through all FDF members but chose to focus on food manufacturers because they weren't directly affected by the levy.
Clark said CFC already knows the position of most of the drink-producing companies.
"Producers of food aren't directly affected, therefore you might get a more interesting answer," Clark said.
FDF said there has been no change in its position on the soft drinks levy and there is no persuasive evidence that the tax would achieve the stated public health goals.
"We oppose punitive taxation of food and drink on principle," FDF said.
Draft legislation on the soft drinks industry levy will be published Monday in the treasury's draft finance bill, and Clark said he hopes FDF take the chance to "press the 'reset' button".
"Instead of opposing the tax, FDF could be helping more companies to follow the lead of Tesco and Lucozade Ribena Suntory and commit to reduce the sugar in all of their soft drinks below the 5 grams per 100ml threshold that would trigger the tax."
"We will study the draft [legalisation] with great interest and will continue to make appropriate representations in support of the positions outlined above.”