Most of the halachic discussion regarding the obligation of married women to cover their hair has focused on the proper types of coverings to fulfil the Misva. However, there has even been some discussion whether the obligation is applicable at all nowadays. Hacham Shalom Masas, the late Chief Rabbi of Yerushalayim, originally from Casablanca, presents a detailed series of Teshuvot (responsa) in his Tevuot Shemesh (Even HaEzer, 137-139). It is highly recommend reading these Teshuvot and enjoying the various opinions he brings. He opens Teshuva 138 by outlining the extreme opinions, at opposite poles: Those who hold that the Halacha is not applicable nowadays, and on the other hand, the opinion of Hacham Ovadia and others that even covering with a wig is not sufficient. The Hod Yosef, Hacham Yosef Masas, attempted to marshal proofs from early sources that this Halacha is no longer applicable. Hacham Masas methodically goes through the proofs and refutes each one. His overwhelming conclusion is that the broad consensus of all the Poskim is that the prohibition remains intact.
One of the arguments of the Hod Yosef questions how can a Torah prohibition be derived from the Pasuk regarding a Sotah that states the Kohen uncovers her hair, implying that, in general, a married woman’s hair must be covered. He brings the Gemara in Masechet Shabuot (35a) that establishes that a Torah prohibition cannot be derived from an implication of the text, but only from a direct statement.
Hacham Shalom categorically refutes this argument. He demonstrates that the Gemara only means that a bona-fide Misvat Lo Ta’aseh or Misvat Aseh (negative or positive commandment) cannot be derived from an implication. However, many times, a Torah prohibition is learnt from an implication. For example, "Hasi Shiur Asur Min HaTorah"-the Torah prohibition of eating less than a Kezayit (olive bulk) of a forbidden food is derived from an implication. While it is not subsumed in the negative commandment, it remains a Torah prohibition. Therefore, while there is no official Misvat Aseh or Lo Ta’aseh regarding covering hair, there is still a Torah prohibition. Hacham Shalom cites this as the opinion of Hacham Ovadia in Yabia Omer (Even HaEzer 4:3).
Another argument of the Hod Yosef is based on the Talmudic principle that if the reason behind a Gezerah (Rabbinic decree) no longer applies, the Gezerah is annulled. He cites an example of the Gezerah not to drink from "Mayim Megulim"-water left out uncovered overnight, out of concern that a snake may have secreted venom into the water. Many Poskim say that nowadays snakes are not common, and therefore the Gezerah is annulled. The Hod Yosef wanted to extrapolate from this that since the norm today is not for women to cover their hair, not covering the hair is no longer a breach of modesty and there is no longer a prohibition.
Hacham Shalom vehemently opposes this reasoning and makes the sharp distinction between a Gezerah D’Rabanan, which is inherently based on a specific rationale and a Misva of the Torah, which is the infinite wisdom of the Creator and is not subject to change.
These are two arguments of the Hod Yosef. It is important to realize that the opinion of the Hod Yosef is considered a lone opinion, and his arguments have been refuted. The overwhelming majority of Poskim hold that married women are obligated to cover their hair, and the Halachic discussion focusses on how to best fulfil the obligation.
A married woman is obligated to cover her hair.