Slander is spoken, libel is written
It depends on the circumstances.
If the writer is ANOTHER company, trying to lure this associate away from his current employer by saying the owner of his current company is lying, cheating and stealing, then the writer could be sued for libel, and the owner of the company could show malice and damages. The writer, then, would have to use truth as a defense - although truth does not always win a libel case where damages and malice are shown.
If, however, the writer is merely passing on information he heard, or read, to a friend (who happens to be an associate of the company where the owner is supposedly lying and cheating and stealing), and the friend left the company based on this information, there would be no libel suit UNLESS the owner found out about it and the owner decided the associate was valuable enough to bring a suit over or if the owner's reputation was damaged to the extent that he lost business.
It really depends on who hears the information, how many people hear the information, and whether the information is true or not. The reasons behind the slanderous or libelous words should be considered, as well.