COMPANIES that make junk food should be banned from advertising in schools, say the NSW Greens, who are also calling for stricter food labelling laws to combat obesity and diet-related illness.

The federal leader, Bob Brown, will join state candidates today to launch a joint state and federal healthy foods policy. It includes mandatory ''traffic light'' labelling of fast food at the point of sale and on food packaging, and labelling to indicate foods containing trans fats, genetically modified organisms, and artificial dyes that are associated with hyperactivity disorders in some children.

The party will also call for a ban on junk food advertising during children's television viewing hours and a ban on any advertising to children in schools by companies which make unhealthy food.

The latter ban is targeted at programs like Maths Online, a free online tutorial program sponsored by McDonald's, which features its branding and is used by 2600 schools nationally.

''Almost one quarter of young Australians are carrying too much fat and have a 78 per cent greater chance of becoming overweight adults and dying younger,'' a Greens upper house candidate, David Shoebridge, said. ''The link between exposure to junk food commercials and childhood weight gains and obesity is real and unequivocal.''