In parallel to the negotiation of international investment agreements to protect foreign investment, intergovernmental organizations have deployed considerable efforts to adopt and implement standards of conduct for business enterprises operating abroad. Despite their informal character under international law, these instruments are increasingly mentioned in international investment agreements and investment arbitration. How can references to informal instruments elaborated by intergovernmental organizations contribute to the imposition of human rights obligations on foreign investors in international investment law? Drawing upon the interactional theory developed by Jutta Brunnée and Stephen J. Toope, this article considers these references as a practice that has the potential to strengthen the normative pull towards compliance with human rights norms. In addition to emphasizing the role of international investment law as a relevant forum to develop a practice surrounding these informal instruments, it assesses whether the use of these instruments by members of a community of practice is intended to establish a genuine sense of obligation and to impose human rights obligations on foreign investors. Even if some instances evidence a practice that strengthens such a sense of obligation, most of the references included in international investment agreements and investment arbitration do not render a practice of legality.