US health officials are trying once again to crack down on the marketing of tobacco products to children and teens. National limits on vending machine sales and free samples could change the way tobacco is advertised. Under the FDA's rules, tobacco companies may no longer use brand names to sponsor certain events. Advertising that can be seen by children must also be in black-and-white. Officials tried similar measures over a decade ago, but the supreme court ruled in favor of tobacco manufacturers. Tobacco companies argue that restrictions are unconstitutional, but a US district court judge has now backed most limits.