If the supplier tapes that same phone conversation without the manager's permission, he runs afoul of Pennsylvania law. Knowing the law before taping is more than a good idea. Recordings made illegally have few uses and can led to serious legal trouble. In court, a recording can be direct proof in certain instances. And, the power of a recording to impeach previous testimony has been aptly demonstrated.
Timely recordings work to ward off lawsuits too.
If an employee threatens a sexual harassment suit, for example, a recording contradicting the claim could persuade her that she is unlikely to win in court. Or, if federal regulators investigate sexual discrimination at the facility, a recording could prove otherwise. Other uses include defending or explaining administrative practices to the Board, maintaining a clear record of events, and jogging personal memory. Tape unwisely and lose the trust of those who associate secret taping with unethical behavior. But open discussion often dwindles if taping is announced.