An employer who permits the entry upon premises occupied by him or under his control of a laborer or an assistant hired by an employe or contractor who has rejected article three of this act, for the performance upon such premises of a part of the employer's regular business entrusted to such employe or contractor, shall be liable to such laborer or assistant in the same manner and to the same extent as to his own employe.
77 P.S. § 1303