77 Pa. Stat. § 461
A contractor who subcontracts all or any part of a contract and his insurer shall be liable for the payment of compensation to the employes of the subcontractor unless the subcontractor primarily liable for the payment of such compensation has secured its payment as provided for in this act. Any contractor or his insurer who shall become liable hereunder for such compensation may recover the amount thereof paid and any necessary expenses from the subcontractor primarily liable therefor.
For purposes of this subsection, a person who contracts with another (1) to have work performed consisting of (i) the removal, excavation or drilling of soil, rock or minerals, or (ii) the cutting or removal of timber from lands, or (2) to have work performed of a kind which is a regular or recurrent part of the business, occupation, profession or trade of such person shall be deemed a contractor, and such other person a subcontractor. This subsection shall not apply, however, to an owner or lessee of land principally used for agriculture who is not a covered employer under this act and who contracts for the removal of timber from such land.
77 P.S. § 461