Rowan vs US Post Office Department
Rowan v. Post Office Dept., 397 U.S. 728 (1970)
[ Case text and audio here ]
Introduction
A major, and probably most relevant case, is Rowan vs US Postal Service ('Rowan') and was decided in 1970. It is based on a challenge to a provision in 39 U.S.C. § 4009 (now § 3008) called: 'Prohibition of pandering advertisements' (here).
39 U.S.C § 3008 states that:
"Any pandering advertisement which offers for sale matter which the addressee in his sole discretion believes to be erotically arousing or sexually provocative shall be subject to an order of the Postal Service to refrain from further mailings of such materials to designated addresses thereof."
The USPS empowers addressees to inform the USPS to cease delivery of pandering advertisements via a Prohibitory Order. The USPS in turn informs the sender to cease any subsequent delivery, and remove the addressee from its mailing lists (as well as prohibit the sale of lists with addressee information on it). This is effectively a '2-hop opt-out' scheme where an addressee informs the USPS, and the USPS subsequently informs the mailer to cease mailing.
While the case was decided in 1970, the USPS still offers USPS form ps-1500: 'Application for Listing and/or Prohibitory Order" (here). Note that it specifically mentions 'unwanted sexually oriented advertising', however, subsequent courts have held that it is the sole discretion of the addressee to decide if material is sexual in nature or not.
Summary
In short, the sole determination as to whether the literature you receive is objectionable or not is within your discretion, and you are not to be second-guessed in that discretion.
This notion was challenged by players in the mail order business as unconstitutional and infringing on their right to communicate.
The case
The Supreme Court however held that:
"Weighing the highly important right to communicate, but without trying to determine where it fits into constitutional imperatives, against the very basic right to be free from sights, sounds, and tangible matter we do not want, it seems to us that a mailer's right to communicate must stop at the mailbox of an unreceptive addressee."
And to solidify the ruling:
"In effect, Congress has erected a wall -- or, more accurately, permits a citizen to erect a wall -- that no advertiser may penetrate without his acquiescence."
To wit:
"To hold less would tend to license a form of trespass, and would make hardly more sense than to say that a radio or television viewer may not twist the dial to cut off an offensive or boring communication, and thus bar its entering his home. Nothing in the Constitution compels us to listen to or view any unwanted communication, whatever its merit; we see no basis for according the printed word or pictures a different or more preferred status because they are sent by mail. The ancient concept that "a man's home is his castle" into which "not even the king may enter" has lost none of its vitality, and none of the recognized exceptions includes any right to communicate offensively with another"
Once in place, the addressee does not have to be burdened by having to keep reviewing subsequent mailings to determine whether they now pass muster:
"The continuing operative effect of a mailing ban, once imposed, presents no constitutional obstacles; the citizen cannot be put to the burden of determining on repeated occasions whether the offending mailer has altered its material so as to make it acceptable."
And finally:
"We therefore categorically reject the argument that a vendor has a right, under the Constitution or otherwise, to send unwanted material into the home of another.
The decision in Rowan was largely build on a previous case from 1943 called 'Martin vs City of Struthers'
[ Fun fact: The banner message around the stickers edge shows the court case number and the exact wording of the Court's finding: "A vendor does not have a constitutional right to send unwanted material into someone's home, and a mailer's right to communicate must stop at the mailbox of an unreceptive addressee" ]