Usually, if you "call upon" a person or group of people, you are asking them for their assistance or support. So, whilst you may "call upon teachers to be judges", it is unlikely that you would "call upon the teachers to come down from the staff office", unless perhaps they were staging some kind of protest and had locked themselves in it. ", or "call upon the people of the country", or "call upon the Transport minister...
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.