The particular definition of skilled and unskilled workers, as you asked, is not given. Still, I am sending you the definition of a worker:
"Worker" means a person employed, directly or by or through any agency (including a contractor) with or without the knowledge of the principal employer, whether for remuneration or not, in any manufacturing process, or in cleaning any part of the machinery or premises used for a manufacturing process, or in any other kind of work incidental to, or connected with, the manufacturing process, or the subject of the manufacturing process but does not include any member of the armed forces of the Union: