Question: There are Muslim women working in factories wearing trousers and not covering their heads. Because that’s how it is in Europe, and it is not easy to make ends meet. If a Muslim woman is working under these conditions to make a living and save money, what would Islam’s ruling be about this?
For a woman, it is obligatory to cover her body when she is around other men, except the family members who are forbidden to marry her. Face, hands up to the wrist joints and feet up to the ankle joints are exceptions from the body. Because while working, it becomes unavoidable to uncover hands and face. Regardless of gender, it is everyone’s duty to work and earn. According to a hadith, “It is obligatory for every Muslim man and woman to seek a way of earning.”  Because, all Muslims need to have an income in order to fulfill their responsibilities.
It is forbidden for a Muslim woman to work revealing her body parts which she is obliged to cover. However her income, which she gained through working that way, is not unlawful because she earned it in return of her work/effort. So, she would be sinful since she didn’t observe the hijab  while working, but her income is not considered to be unlawful.
“Regarding women wearing trousers; they can wear shalwar/baggy trousers which do not reveal the parts or form of their bodies. However, wearing tight trousers etc. which reveals women’s body forms is disliked (makruh).” 
If a woman wears tight trousers revealing the hip, that would be not only disliked, but also forbidden (haraam). Breasts and hips are of the “beautiful parts (zeenat)” of women that are mentioned in the following verse. They must always be well-hidden, so that men cannot notice:
“Tell the believing women to reduce some of their looks, and cover their private parts. Tell them not to uncover their beauty except what is naturally seen. Tell them to put their headscarves onto their chests and not expose their beautiful parts except to their husbands, their fathers, their husbands’ fathers, their sons, their husbands’ sons, their brothers, their brothers’ sons, their sisters’ sons, their women, those in their possession, those male attendants that have no sexual desire to women, or children who are not yet aware of the private aspects of women. And tell them not to stamp their feet on the ground for their beautiful parts to be noticed.” (An-Noor/ The Light 24:31) Tabarani, Mu’jam al-Awsat, 9/277-278  The traditional dress code of Muslim women, calling for the covering of the entire body except the face, hands, and feet.  Abdul-Hamid al-Shirwan, Ibn Qasim Shihabuddin Ahmad b. Qasim al-Abbadi, Hawashi Ahmed b. Kasım el-Abbadi, Hawas ala Tuhfat al-Muhtaj bi-Sharh al-Minhaj, al-Maktabat al-Islamiyya, Istanbul, ty., v:2, p:112.)