Wiktionary
counteradvertising
n. A form of advertising that aims to dissuade consumers from a product or service.
Wikipedia
Counteradvertising
Counteradvertising is “ Advertising that takes a position contrary to an advertising message that preceded it. Such advertising may be used to take an opposing position on a controversial topic, or to counter an impression that might be made by another party's advertising.” Counteradvertising is often seen informally on controversial topics like smoking.