Women have to cover their faces in front of non-mahram men according to the more correct of the two scholarly opinions, because of evidence that has been explained in the answer to question no. 11774.
Many of the fuqaha’ who do not think that the face is ‘awrah are of the view that it must be covered if there is the fear of fitnah, and when there is a great deal of corruption.
The husband is enjoined to protect his family and warn them against haraam things. Hence he should strive to convince his wife to cover her face, and if she refuses he should force her to do so and she is required to obey him, because he is telling her to do something that is permissible in her view, and it has to do with his right to protect his honour and she does not think it is haraam.
In the answer to question no. 97125, we explained how couples should deal with issues concerning which there is a difference of scholarly opinion. Among the things that we said there was: With regard to everything that is permissible for her, he has the right to prevent her from doing it or make her follow his opinion if he thinks it is haraam, and she must accept that if her doing it will cause harm to her husband and expose him to humiliation or disrespect. For example, covering the face is an issue concerning which the scholars differed, but there is no one who says that it is haraam to cover the face. If she thinks that it is acceptable to uncover the face, he has the right to prevent her from showing it before non-mahrams, and he has the right to make her follow his opinion, which is that it is obligatory to cover the face – which is the more correct view – and she does not have the right to go against him. She will be rewarded for doing that if she seeks reward for obeying her Lord by obeying her husband and does that which is more concealing.
Moreover we say: what is preventing the wife from covering her face and protecting herself from the gaze of those who would stare at her? It is well known that the face is the focus of beauty and the source of fitnah, and the first thing that attracts the gaze. If she thinks that it is mustahabb and not obligatory, there is nothing wrong with doing what is mustahabb and brings one closer to one’s Lord and pleases the husband, and makes her more like the believing women such as the wives of the Prophet (peace and blessings of Allaah be upon him) and the wives of the Sahaabah.
Every believing woman should be keen to cover in this manner, and should hasten to do it, and to praise Allaah for having caused her husband to tell her and encourage her to do it.
We ask Allaah to enable us all to do that which He loves and is pleased with.
And Allaah knows best.