A Labour Government would be "minded to" halt any badger culls under way if it won the next general election.
Shadow environment secretary Mary Creagh told a conference fringe meeting in Manchester that her position on badger culling had changed from a year ago.
"I have certainly moved on from this last year when I was in frame of considering that we would have to continue with the cull," she said at the NFU-Food and Drink Federation event.
"The more I have looked at the science, the less effective I think this cull is going to be. I am really worried about it," she said.
Natural England has licensed a badger cull in west Gloucestershire, with a start date expected within weeks.
A second in West Somerset likely to be given the go-ahead shortly. If deemed safe, up to 40 cull zones could be given the go-ahead.