According to a report published by NHK news Web on June 13, the Tokyo2020 Organising committee has decided that Olympic venues need to be build with domestic building materials "for environmental protection". According to the report, the IOC requires organizers to take the environment into account, however the Japanese organizers seem to have given this a twist to block out environmental-friendly solutions from abroad. If used, the measure would make a first, since procurement standards were explicitly set after the London Olympics. 

Source: 東京五輪 競技場建設の木材は国産優先