Welcome to BYC! How old are these birds and how much space are they in? I would watch them carefully to see if there is one bird who is instigating this behavior and if so, pull that bird out for an extended time out, like a week. Then put her back in and see how it goes. If they are in a coop/run all the time then make sure to add plenty of distractions like flakes of alfalfa to scratch apart, toss in some scratch or meal worms with the hay for more foraging opportunity, dry leaves to scratch through, that type of thing. Ideally time spent out of the coop/run in a large yard or pasture.