Regulations Governing the Establishment and Operation of Offshore Shipping Centers Article 8

Foreign vessels with permission to sail directly between the Offshore Shipping Centers and ports of the Mainland Area may not carry any cargo from the Taiwan Area that is destined for the Mainland Area, or cargo from the Mainland Area that is destined for the Taiwan Area.
中文原文 境外航運中心設置作業辦法第8條
經許可直接航行於境外航運中心與大陸地區港口間之外國船舶,不得載運臺灣地區以大陸地區為目的地或大陸地區以臺灣地區為目的地之貨物。

English translation for reference only; the Chinese text prevails. Not legal advice.