The LME said this week it would look more closely at "discounted" cobalt that came to the trading floor.
Global Witness supply chain expert Sophia Pickles said in a panel session at the LME metals seminar the plan risked targeting the wrong people.
"You risk creating a blunt instrument that may have negative unintended consequences, particularly penalising artisanal mining," she said.
Speaking on a panel for LME Week, Pickles also highlighted how existing checks on responsible sourcing were not totally effective.
"They don't guarantee that the company is sourcing responsibly, and they aren't a substitute for your own individual responsible sourcing assessment," she said.
Global Witness had said in a statement earlier in the day that the LME was...