Under the international law of treaties, reservation is a unilateral statement, however phrased or named, made by a State when signing, ratifying or acceding to a treaty, whereby it purports to exclude or to modify the legal effect of certain provisions of the treaty in their application to that State. As a matter of well-established principle, ILO Conventions may not be ratified subject to reservations. Although Conventions contain various flexibility clauses, including some that specifically enable ratifying States to limit or qualify the obligations assumed on ratification, no limitations on the obligations of a Convention other than those specifically provided for are possible. 

The inadmissibility of reservations, as explained in the 1951 Memorandum to the International Court of Justice in the Genocide Case, is based on the premise that “the rights which the treaties have conferred on non-governmental interests in regard to the adoption of international labour Conventions would be overruled if the consent of governments alone should suffice to modify the substance and detract from the effect of the Conventions”.

Contrary to reservations, interpretative declarations are permissible. Interpretative declarations do not intend to exclude or modify the scope of certain obligations arising from a Convention but simply to put on record the Member’s understanding of a particular provision. In registering a ratification accompanied by an interpretative declaration, the ILO Director-General generally indicates that the understanding does not in any way qualify the acceptance by the Member concerned of the obligation to make effective the provisions of the Convention but simply constitutes a formal record of the interpretation that the Member attaches to the Convention. The use of interpretative declarations or understandings remains fairly limited; recent instances include the interpretative declarations attached to the ratification of the Indigenous and Tribal Peoples Convention, 1989 (No. 169) by Denmark in 1996, the Worst Forms of Child Labour Convention, 1999 (No. 182) by the United States in 1999, and the Labour Relations (Public Service) Convention, 1978 (No. 151) by Brazil in 2010.