A seatback portion has a tether passageway defined therein from proximate an upper section to proximate a lower section thereof. A seatbelt tether includes a tensioning mechanism, a tether ring and a connecting portion that extends from the tether ring to the tensioning mechanism. The connecting portion extends through the tether passageway with the tether ring located at the upper section outside the seatback portion. The tether ring is shaped and dimension to slide-ably receive a seatbelt. The tensioning mechanism selectively applies tension to the tether ring. In a non-tensioned state the tether ring is movable to an upper outboard side of the seatback portion. In a tensioned state the tether ring is pulled toward a headrest supporting section of the seatback portion inboard and away from the upper outboard side of the seatback portion.