The most known experiment with subliminal messaging was conducted by a marketing researcher and psychologist James Vicary in 1957 during the presentation of the movie Picnic. Every 5 seconds the words "Hungry? Eat popcorn. Drink Coca Cola"
were projected for 0.003 seconds. That is extremely fast. What you see
in the picture on the left, for example, flashes for 0.04 seconds. Sales
of popcorn and Coke in that New Jersey theater increased 57.8 percent
and 18.1 percent respectively. Numerous scientific researches following
these experiments confirmed beyond any doubt that subliminal messaging
works. When advertising industry and government agencies understood the
potential of subliminal messaging they started investing millions in
developing and perfecting of subliminal techniques, which can be used
not only for marketing, but also for propaganda and mind control.

http://subliminalmanipulation.blogspot.com/

Shortly after these adverts (and others) came out Wilson Bryan Key Released a book called “Subliminal Seduction
” which showed various uses of subliminal messages as used by advertisers.
This book further heightened public concern and led to the FCC to
investigate in 1974. This investigation concluded with a statement from
them:

subliminal advertising is contrary to the public interest
and intended to be deceptive, and that any [tv] station employing them
risks losing its liscence.

The TV stations did not try and resist, they represented the
interests of their viewing audience, and if subliminal messages were
deceptive then they wanted them off the air too.
Subliminal advertising was also banned in Canada following the
broadcasting of Hūsker Dū? ads there in 1974. Shortly afterwards the UK,
Australia, and Europe also followed suit.
http://www.subliminal-messaging.com/when-and-why-was-subliminal-messaging-banned/