72 Pa. Stat. § 7239
The department may, by regulation, authorize or require particular categories of vendors selling tangible personal property for resale to precollect from the purchaser the tax which such purchaser will collect upon making a sale at retail of such tangible personal property: Provided, however, That the department, pursuant to this section, may not require a vendor to precollect tax from a purchaser who purchases for resale more than one thousand dollars ($1,000) worth of tangible personal property from such vendor per year. In any case in which a vendor has been authorized to prepay the tax to the person from whom he purchased the tangible personal property for resale such vendor so authorized to prepay the tax may, under the regulations of the department, be relieved from his duty to secure a license if such duty shall arise only by reason of his sale of the tangible personal property with respect to which he is, under authorization of the department, to prepay the tax. The vendor, on making a sale at retail of tangible personal property with respect to which he has prepaid the tax, must separately state at the time of resale the proper amount of tax on the transaction, and reimburse himself on account of the taxes which he has previously prepaid. Should such vendor collect a greater amount of tax in any reporting period than he had previously prepaid upon purchase of the goods with respect to which he prepaid the tax, he must file a return and remit the balance to the Commonwealth at the time at which a return would otherwise be due with respect to such sales.
72 P.S. § 7239