Related Rule
Practice Relating to Rule 19. Control during the Execution of Attacks
Switzerland’s Basic Military Manual (1987) states: “If the military advantage is disproportionate to the damage, [commanding officers at the battalion or group level, and those of higher ranks,] must cancel or suspend the attack.” 
Switzerland, Lois et coutumes de la guerre (Extrait et commentaire), Règlement 51.7/II f, Armée Suisse, 1987, Article 29(2).
Switzerland’s Regulation on Legal Bases for Conduct during an Engagement (2005) states:
165 The following precautionary measures must be taken into consideration when making decisions, when issuing orders and in particular when conducting military operations.
167 If it becomes apparent that an attack is directed against an objective that is not military or against a protected object or that the attack causes disproportionate damage to the civilian population or its property in relation to a concrete and direct military advantage, the attack must be stopped immediately. 
Switzerland, Bases légales du comportement à l’engagement (BCE), Règlement 51.007/IVf, Swiss Army, issued based on Article 10 of the Ordinance on the Organization of the Federal Department for Defence, Civil Protection and Sports of 7 March 2003, entry into force on 1 July 2005, §§ 165 and 167. The German language version notes in § 167: “… or that the attack causes disproportionate damage to the civilian population and [“und”] its property …”.
In 2005, Switzerland withdrew its reservations to Articles 57 and 58 of the 1977 Additional Protocol I. 
Switzerland, Withdrawal of reservations to the 1977 Additional Protocol I, 17 June 2005.