Pope Paul VI
Mense Maio §13
Mense Maio: On Prayers During May for Preservation of Peace
13 We ask you, Venerable Brothers, to make known Our wishes and Our urgent pleas to the faithful entrusted to your care, in whatever way you deem most suitable. We also ask that you make provisions for special prayers in every diocese and parish during the month of May; in particular, on the feast of the Queenship of Mary, let there be solemn public prayer for the intentions We have mentioned.
Source: Mense Maio (Vatican.va)