(d) In which his unemployment is due to a stoppage of work, which exists because
of a labor dispute (other than a lock-out) at the factory, establishment or other
premises at which he is or was last employed: Provided, That this subsection
shall not apply if it is shown that (1) he is not participating in, or directly
interested in, the labor dispute which caused the stoppage of work, and (2) he is
not a member of an organization which is participating in, or directly interested
in, the labor dispute which caused the stoppage of work, and (3) he does not
belong to a grade or class of workers of which, immediately before the
commencement of the stoppage, there were members employed at the premises
at which the stoppage occurs, any of whom are participating in, or directly
interested in, the dispute.