يَا أَيُّهَا الَّذِينَ آمَنُوا لَا يَسْخَرْ قَوْمٌ مِّن قَوْمٍ عَسَىٰ أَن يَكُونُوا خَيْرًا مِّنْهُمْ وَلَا نِسَاءٌ مِّن نِّسَاءٍ عَسَىٰ أَن يَكُنَّ خَيْرًا مِّنْهُنَّ ۖ وَلَا تَلْمِزُوا أَنفُسَكُمْ وَلَا تَنَابَزُوا بِالْأَلْقَابِ ۖ بِئْسَ الِاسْمُ الْفُسُوقُ بَعْدَ الْإِيمَانِ ۚ وَمَن لَّمْ يَتُبْ فَأُولَٰئِكَ هُمُ الظَّالِمُونَ
O you who believe! Let not a group ridicule at another group, it may be that the latter is better than the former. Nor let (some) women scoff at other women, it may be that the latter is better than the former, nor defame one another, nor insult one another by nicknames. How bad is it, to insult one's brother after having Faith. And whosoever does not repent, then such are indeed Dhalimoon. (49/11)
Our brother, Abū al-ʿAbbās Mūsá Richardson while mentioning the explanation of the aforementioned verse, discusses the actions done by some sisters in the way the deal with others who don’t wear the niqaab; whether they don’t wear it following a specific school of thought, position of a scholar or general lack of study on the issue. This segment also discusses the affiliation founded upon garments (i.e. groups, forums, mailing lists, etc, specific for those who adorn the garment of niqaab) Sisters! You are bound together by an ʿaqīdah and a manhaj, not a veil! This issue is further exasperated considering the majority of ʿulamāʾ historically, have not held the niqaab to be obligatory but rather recommended, so perhaps caution and care is needed when giving da'wah to one another.
From the Tafsīr Course ’07, Sūrah-Hujaraat.