One of my favorite stories is about a run-in the writer Rose Wilder Lane had with the federal government in the 1940s. (Weird but true: Lane was the daughter of Laura Ingalls Wilder, author of the Little House on the Prairie children’s books. Lane also was a noted political thinker and, at 74, the oldest female correspondent covering the Vietnam War.)

Lane had written a postcard critical of Social Security. The local postmaster decided this was subversive, and turned it over to the FBI, which asked the police to investigate. Lane — who was a small woman — was confronted while weeding her daisies by a strapping (and armed) state trooper who accused her of “subversive activity.” She drew herself up to her full height, dressed him down soundly for violating her rights as a citizen — and then invited him in for cookies.

The story became front-page news around the country, thanks to an article called “What is this, the Gestapo?” Although the story’s sweet and funny, it has a bite. The real issue — as relevant now as then — has to do with the role of a common carrier (in this case the post office) when dealing with a real or suspected crime. As one of my commentators pointed out to a post in a previous column, the USPS does indeed investigate mail fraud — defined as cases in which the mail service is used for the commission of a crime).

However, this is not the same thing as “routinely opens and reads mail.” In fact, doing so is expressly unconstitutional, as decided by the Supreme Court in an 1877 case, during which the court decreed, "No law of Congress can place in the hands of officials connected with the Postal Service any authority to invade the secrecy of letters and such sealed packages in the mail” (See here for full details on the case.)

This isn’t merely a case of civil liberties run amok. Allowing (or requiring) the government to censor or control communications is a tool of social oppression. Keep in mind that prior to the Civil War, postmasters in the South routinely refused to deliver abolitionist literature, on the grounds that it was “illegal.”

The point? It’s unconstitutional (at least in principle) to permit — much less require — entities that serve in the role of “common carriers” to investigate or otherwise interfere with the contents of the communications they’re carrying.