Angry mothers are staging supermarket sit-ins in an effort to force a national recall of a brand of baby formula they claim contains unlabelled genetically modified products.

Eight mothers this morning stormed the Coles supermarket in Fitzroy, Melbourne, and 15 are protesting at a Woolworths store in Sydney's Neutral Bay.

The groups cordoned off a display for breast milk replacement S-26 Soy and demanding the product be removed from shelves.

The action follows two tests commissioned by Greenpeace Australia Pacific that allegedly revealed trace elements of genetically modified organisms (GMOs), which are not labelled on the product.