Definition:
The bar associations in many U.S. states are voluntary. That is, attorneys do not have to join the bar association to practice law in that state. Voluntary bar associations do not regulate the practice of law in that state nor do they admit lawyers to practice law within the state. The opposite of a voluntary bar association is a unified bar association.
States which have voluntary bar associations include Vermont, Maine, New York, Pennsylvania, Maryland, Delaware, Massachusetts, Ohio, Indiana, Illinois, Iowa, Minnesota, Tennessee, Arkansas, Kansas, and Colorado.
Most U.S. states have unified bar associations, which require that attorneys join the bar in order to be able to practice in that state.
