Frank Zappa called them the "Mothers of Prevention," the group of wives married to members of Congress who decided in the mid-80s to go to war against rock lyrics and whip up some good ol' conservative hysteria. Zappa himself had earlier testified in front of Congress and sparred on the Sunday Beltway shows like Crossfire.
Anyway, Tipper Gore's Parents Music Resource Center (PMRC) produced a list of the "Filthy Fifteen," including songs like Sheena Easton's "Sugar Walls" and Madonna's "Dress You Up," which either contained lyrics "promoting" violence, sexual references, drug and alcohol, and Satan's favorite, the "occult."
This last category became increasing popularity during the '80s of heavy metal music, which was often invoking Satan in its lyrics, or creating occult-like atmospheres in its production.
This campy, horrorshow culture ran right into the growing power of conservative Christians and evangelical preachers who made a *lot* of money whipping up "Satanic Panic" among their national flock.
They listened to rock records backwards, believing they heard subliminal messages, and looked at the rising teenage suicide rate and used heavy metal as a scapegoat, instead of family breakups, drug abuse, economic uncertainty, and increasing access to guns.
Of course, none of this would have gone much further than churches if it wasn't for Ted Koppel, Barbara Walters, Geraldo Rivera, et al who were fanning the flames of this fire.
The warning label itself appeared in 1990, just as rap was taking off and a new lyrical boogeyman appeared.