Соответствующая норма
Practice Relating to Rule 18. Assessment of the Effects of Attacks
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.
Switzerland’s ABC of International Humanitarian Law (2009) states:
The principle of proportionality applies to every aspect of the conduct of hostilities. … Before launching an attack there is an obligation to assess whether or not the impact on the civilian population is excessive in relation to the concrete and direct military advantage anticipated. 
Switzerland, Federal Department of Foreign Affairs, ABC of International Humanitarian Law, 2009, pp. 13–14.