Which of these countries is not member Arab Maghrab Union?

Egypt
The Maghreb is usually defined as much or most of the region of Northwest Africa, west of Egypt. The traditional definition as being the region including the Atlas Mountains and the coastal plains of Morocco, Algeria, Tunisia, and Libya, was later superseded, especially since the 1989 formation of the Arab Maghreb Union, by the inclusion of a fifth nation, Mauritania, and of the disputed territory of Western Sahara.