While a PhD is becoming increasingly common and often preferred for tenure-track positions teaching business at the university level, it's
not strictly required. Many universities, particularly smaller ones or those with a focus on teaching rather than research, may hire instructors or lecturers with a Master's degree and significant professional experience in business. These positions are often not tenure-track.
For tenure-track positions, particularly at research-intensive universities, a PhD is almost always required. The PhD demonstrates the candidate's ability to conduct original research and contribute to the field's scholarly knowledge.
In short: A Master's degree *might* suffice for some teaching positions, but a PhD significantly increases the chances of securing a tenure-track position at a university.