Works contract tax doubt

Dear Experts, Can u please tell me the "point of Taxation" of Works contract Tax. For instance, In my company(pvt ltd) we are purchasing materials from one vendor & given to another vendor, he is only doing labour work(service only) for our new building construction work. My doubt is whether i have to deduct Works contract tax in that labour bill or not? or WCT is applicable only if the bill contains materials and labour?