" (3) A settlement arrived at in the course of conciliation proceedings under this Act (or an arbitration award in a case where a notification has been issued under ,sub section (3A) of Section (10A) or (an award of a Labour Court, Tribunal or National Tribunal) which has become enforceable shall be binding on (a) all parties to the industrial dispute; (b) all other parties summoned to appear in the proceedings as parties to the dispute, unless the Board, (arbitrator) (Labour Court, Tribunal or National (1) (2) [1964]S.C.R. 448. 878 Tribunal), as the case may be, records the opinion that they were summoned without proper cause; (c) where a party referred to in clause (a) or clause (b) is an employer, his heirs, successors or assigns in respect of the establishment to which the dispute relates; (d) where a party referred to in clause (a) or clause (b) is composed of workmen, all persons who were employed in the establishment or part of the establishment, as the case may be, to which the dispute relates on the date of the dispute and all persons who subsequently become employed in that establishment or part.