Sec. 4. (a) A physician shall designate a member state as the state of principal license for purposes of registration for expedited licensure through the compact if the physician possesses a full and unrestricted license to practice medicine in that state and the state is:
(1) the state of primary residence for the physician;
(2) the state where at least twenty-five percent (25%) of the physician's practice of medicine occurs;
(3) the location of the physician's employer; or
(4) if no state qualifies under subdivision (1), (2), or (3), the state designated as state of residence for purposes of federal income tax.
(b) A physician may redesignate a member state as the state of principal license at any time, as long as the state meets the requirements in subsection (a).
(c) The interstate commission is authorized to develop rules to facilitate redesignation of another member state as the state of principal license.