(4) may commence a civil action against the person to whom such order was issued to require compliance with such order. The appropriate United States district court shall have jurisdiction, without regard to the amount in controversy or the citizenship of the parties, to enforce such order. (C) Award of costs authorized The court, in issuing any final order under this paragraph, may award costs of litigation (including reasonable attorney and expert witness fees) to any party, whenever the court determines such award is appropriate. (D) Mandamus proceedings Any nondiscretionary duty imposed by this section shall be enforceable in a mandamus proceeding brought under section 1361 of title 28, United States Code. (d) Limitation of preemption Nothing in this Act shall be construed— (1) to limit the ability of members of a labor organization to remove their elected or appointed officials through a democratic election conducted among such members