Some grassroots members of Manitoba's governing New Democrats are pushing for a tax on junk food, but newly released documents show the party has long held off on the idea.

Briefing notes and other material obtained by the Canadian Taxpayers Federation reveal the government has been monitoring fat taxes overseas as well as studies on the issue, but has found problems.

"Health-related food taxes continue to be discussed as a policy option for obesity prevention and for addressing other health goals, " reads a discussion paper from June 2012 prepared by Paul Fieldhouse, a policy analyst in the Department of Healthy Living.

"A major problem confronting any food tax proposal is scientific uncertainty about the complex nature of relationships between diet and health."

In the same year, a note from Fieldhouse points out that Denmark was driven to repeal its tax on fatty foods because businesses complained it was an administrative nightmare and threatened jobs.

And going as far back as 2008, Fieldhouse writes that "there is only, at best, weak evidence that junk food taxes would be effective in achieving public health goals of influencing food choices."

The taxpayers federation released the documents Wednesday because the issue is tentatively on the agenda for this weekend's annual NDP convention. One of the party's constituency associations is seeking a "healthy living levy" of an unspecified amount that would raise money for school nutrition programs and other initiatives.

"It's disturbing that this idea keeps coming up because the government research .... shows that these taxes don't work," federation spokesman Colin Craig said.

"It seems to be about revenue and sort of micro-managing the lives of Manitobans."

Finance Minister Jennifer Howard flatly rejected the idea Wednesday.

"We will not be introducing any kind of tax on what is considered junk food," Howard said.

"This is an interesting idea ... and we certainly ask questions about it, but it's not something we're going to pursue."

The idea of taxing sugar-sweetened beverages seems to have been under active discussion in the fall of 2012, when Fieldhouse wrote: "Just so folks know, Manitoba has been looking at this, but nothing I can share right now outside one-to-one private discussions."

Again, Howard said, the idea is not going anywhere.

"It's hard to implement and it's not something that actually achieves the goal of ensuring that people make healthier food choices."