I think the "traditional" use of wiretapping, prior to the 1968 law, was _de facto_, not _de jure_. The cops just wiretapped whomever they felt needed wiretapping. (For evidence of this, from the FBI to NSA, see books on Hoover's era, and Bamford on the NSA. For local cops, I have no immediate source, but note that "wire men" did not suddenly spring into existence in 1968...wiretapping has been used for many years.) The increased focus on civil rights (some would disagree with this characterizaton...) with the "Miranda rights" and "authorized wiretap" trends of the 1960s forced these practices to be formalized. More or less. There was a Supreme Court ruling in 1967 (I don't have the citation handy) that held that wiretaps constituted an illegal search and seizure. The Federal wiretap statute (18 U.S.C. 2510 et seq., later amended by the ECPA) was a direct response to this ruling. Until then, wiretaps were barred from Federal use by the Federal Communications Act, and not by 4th Amendment considerations (Nardone v. United States, 320 US 379 (1937)). But that was a question of admissibility of evidence, and in 1953 (Schwartz v. Texas, 344 US 199) the Court ruled that that was not binding on state courts. As a sidenote, the first act regulating police wiretaps was in New York in 1942; in 1895, the state had passed a law prohibiting wiretaps completely.