עַל `al "upon, because of, against". Most often used in the prophets to indicate those spoken "against".
In Am 1:3ff. it is used three times in each oracle of the reason "for three rebellions, for four... because they...".
The expression עַל־פְּנֵי "across the face of..." is used in the hymn fragments (5:8; 9:6) cf. the similar phrase in 9:8.