The fact that an international agreement exists does not mean that Switzerland is obliged to comply with it; this is only the case once the national ratification process has been completed. Important agreements must be approved by Parliament and are subject to a mandatory or optional referendum.
Accession to collective security organisations or supranational communities (e.g. the European Union) is subject to a mandatory referendum. For example, Switzerland’s accession to the European Economic Area was subject to a mandatory referendum and was rejected by the people and the cantons in 1992.