In South Carolina, who decides what counts as the unauthorized practice of law?
Answered for: South Carolina
SECTION 40-5-310. Practicing law or soliciting legal cause of another without being enrolled as member of South Carolina Bar. No person may either practice law or solicit the legal cause of another person or entity in this State unless he is enrolled as a member of the South Carolina Bar pursuant to applicable court rules, or otherwise authorized to perform prescribed legal activities by action of the Supreme Court of South Carolina. The type of conduct that is the subject of any charge filed pursuant to this section must have been defined as the unauthorized practice of law by the Supreme Court of South Carolina prior to any charge being filed.
The South Carolina section adds a condition that is unusual among the states read here: the conduct charged must already have been defined as the unauthorized practice of law by that state's Supreme Court before a charge is filed.
This answer is true in South Carolina and nowhere else on this site. Another jurisdiction is another answer, or an honest gap: see what has been read for South Carolina.