(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 any of the following:
(1) The state of principal residence for the physician.
(2) The state where at least 25% of the practice of medicine occurs.
(3) The location of the physician's employer.
(4) If no state qualifies under paragraph (a)(1), (a)(2), or (a)(3) of this section the state designated as state of residence for purpose of federal income tax.
(b) A physician may re-designate a member state as state of principal license at any time, as long as the state meets the requirements of subsection (a) of this section.
(c) The Interstate Commission is authorized to develop rules to facilitate re-designation of another member state as the state of principal license.