One group were spotted filling Santa Claus-size sacks with the delicacies in Devon Woodland Trust forest last week.
Country walker Bridgid Hardman said: ‘My husband and I were enjoying a peaceful stroll in the woods when we heard a lot of crashing about.
‘We found these three Chinese looking women carrying sacks and using big knives to slice fungi from trees and off the ground.
‘The sacks were so full they looked like Santas. But the moment we tried to take pictures of them they ran back into cover.
‘It’s really annoying. Nobody minds you foraging for a few mushrooms but these people are hoovering everything up on more like a commercial scale.
‘I don’t think they understand the effect of what they are doing. This is the time of year when a lot of fungi bloom and release their spores to reproduce.
‘Taking everything in sight affects the chances of this new growth. And unless they really know what they are doing there’s always a chance of taking something poisonous by mistake.’
Shaldon-born Bridgid who lives in Dawlish added: ‘They are not just going after fungi. Two years ago similar groups targeted the Teign cockle beds. Today there isn’t a cockle to be found.’
Steve Hussey, of the Woodland Trust, confirmed he had received a complaint about the fungi harvesters’ activities.
But he declined to make any comment about them.