Must a wife wear niqab in front of her paternal or maternal uncles?

A husband instructing his wife to wear niqab in front of her paternal uncle (ʿamm) or maternal uncle (khāl) is a question IslamQA answered directly: she is not obligated to obey such an instruction. The fatwa describes it as tanattuʿ, blameworthy religious over-strictness.

Qur'an 24:31 permits a woman to display her adornment before her mahram relatives. Although paternal and maternal uncles are not individually named in the verse, the fatwa cites classical scholars who place them in the same category as other mahram relatives. Ibn Qudamah, a Hanbali jurist, states that a woman's mahram male relatives may see what ordinarily appears, such as her neck, head, hands and feet. Al-Qurtubi, a Maliki exegete, records that the majority of scholars held that paternal and maternal uncles are like other mahram relatives regarding what they may see. The fatwa also cites the hadith in which the Prophet ℵ told ʿA'ishah to admit her foster-uncle: "Let him in, for he is your uncle." The foster relationship therefore carried the relevant mahram status just as a blood relationship would.

The fatwa's practical advice is not confrontational. A wife should deal gently with her husband rather than openly defy him, and should try to explain the scholarly evidence to him. If he remains insistent and refusing his demand is likely to cause serious marital discord or worsening relations, the fatwa advises her to comply rather than jeopardise the marriage over the matter, even though it expressly regards the husband as mistaken. This practical advice does not alter its underlying ruling that she is not obligated to obey his instruction to cover before her own paternal or maternal uncles.

Source. IslamQA, Question 373247