Consumer groups in the US are suing cereal maker Kellogg's and children's TV network Nickelodeon in a bid to stop them showing adverts for sugary foods.
Kellogg's sweetened cereals are popular with many children
They are demanding that both companies drop TV and website ads for so-called 'junk foods' aimed at youngsters.
TV ads for sugary and fatty snacks have been criticised by pressure groups in the US, who argue they are helping to fuel soaring child obesity rates.
But industry groups deny that food companies have acted irresponsibly.
They say that manufacturers have no direct control over which foods are bought by consumers.
The court action against Kellogg's and Nickelodeon-owner Viacom is being brought jointly by the Center for Science in the Public Interest (CSPI), the Campaign for a Commercial-Free Childhood and two Massachusetts parents.
They point to a recent study by the US government-backed Institute of Medicine, which suggested that companies were using TV ads to encourage more children to eat unhealthy foods.
The groups, which served notice of the lawsuit on Thursday, want Nickelodeon to stop showing ads for treats and snacks when more than 15% of the audience is made up of under-eight-year-olds.
They also want the companies to stop marketing junk foods on websites and through competition giveaways.
"The industry has had decades to clean up its act, but instead it has only intensified its marketing," said CPSI executive director Michael Jacobson.
"Nickelodeon and Kellogg engage in business practices that literally sicken our children," he added.
However, Kellogg's and Nickelodeon said both companies had been encouraging children and families to lead healthy lifestyles.
Kellogg's - whose Tony the Tiger character famously promotes the firm's Frosties sugar-coated cereal - said it was committed to educating parents and children about nutrition and exercise.
Nickelodeon added it actively encouraged families to lead active and healthy lives.
Dan Mindus, a spokesman for campaign group the Center for Consumer Freedom, said: "Kids want these foods not because of ads, but because they're children."