A trust shall not constitute a qualified trust under this section unless under the plan of which such trust is a part—
(A)#
in the case of a participant or beneficiary who is receiving benefits under such plan, or
(B)#
in the case of a participant who is separated from the service and who has nonforfeitable rights to benefits,
such benefits are not decreased by reason of any increase in the benefit levels payable under title II of the Social Security Act or any increase in the wage base under such title II, if such increase takes place after September 2, 1974 , or (if later) the earlier of the date of first receipt of such benefits or the date of such separation, as the case may be.