This phrase refers to the curse like a cloud that spreads to cover the face of the land. The word "face" refers to the surface of the land like a person's face is on the surface of their head. AT: "effects" (See: [[rc://en/ta/man/translate/figs-metaphor]])
This phrase is often translated as “Yahweh says” in the UDB. You can translate this concept whichever way is best in your language. This phrase is used many times in Zechariah.