He may not diminish her food, her clothing or her marital relations (Exodus 21:10)
This verse was written in reference to the Jewish maidservant, whom you will recall was intended to be betrothed. The Torah tells us that, after marrying her, her husband may not marry an additional wife if doing so will decrease the amount of food, clothing or sexual contact that the woman has come to expect. From context, this law is not specific to the Hebrew maidservant, since the previous verse tells us, “she shall be treated like all other girls.” (Rashi there cites the Mechilta specifically referring to this mitzvah.)
The Talmud in Kesubos discusses exactly what the expected parameters of food clothing and sexual relations should be, varying with a husband’s financial level and how physically grueling his profession. (His financial means affect the food she receives, while his profession affects the frequency with which she can expect physical intimacy.)
We see from this mitzvah that a woman has rights in her marriage. These three (food, clothing and physical intimacy) are Biblically mandated that a husband fulfill to the best of his ability. Rabbinically, he has other obligations, such as to pay the value of her kesubah (marriage contract) in the event of his death or divorce, to take care of her medical needs, and to see to her burial if she predeceases him.
This mitzvah applies in all times and all places, but only to men. It is discussed in the Talmud in the fourth and fifth chapters of Kesubos. In the Shulchan Aruch, it is found in Orach Chaim 240. It is #262 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos and #42 of the 194 negative mitzvos that can be fulfilled today in the Chofetz Chaim’s Sefer HaMitzvos HaKatzar.