Yes it is mandatory. According to Sura Alnoor 24:31 which says: And tell the believing women to lower their gaze and protect their private parts(from illegal sexual act), and not to show off their adornment except only that which is apparent( like both eyes for necessity to see the way, or outer palms of hands, one eye or dress like veil, gloves, head cover, apron etc) and to draw their veils all over* JUYUBIHINNA* (i,e their bodies,face,neck and bossoms) and not to reviel their adornment except to their husbands, or their sons, or their husband sons, or their brothers, or their brother's sons, or their sister's sons, or their (muslim) women i,e their sisters in islam, or the( female) slaves, whom their right hand possess, or old male servants who lack vigour, or small children who have no sense of feminine sex. And let them not stamp their feet so as to reveal what they hide of their adornment. And all of you beg Allah to forgive you all, O believers, that you may be successful.
Sura 33 Al-Ahzab Verse 59: O Prophet tell your wives and daughters and the women of the believers to draw their cloaks (veils) all over their bodies(screen their bodies completely except the eyes or one eye to see the way).........
These are the guidelines laid down by our Lord Allah (SWT).
In surah Al-Ahzab it is talking about jilbaab only. Not the face covering. If you keep adding things in brackets () then you modify the meaning.
Could you please please exlpain the word "JUYUBIHINNA" some more withOUT the brackets?