Sati as a practice is outlawed today in India. This is because women were forced to step into the funeral pyre once their husbands died. This practice was stigmatized by Raja Ramohan Roy during the British rule and completely abolished (although in some Indian villages reports of forced sati is documented)
The practice of sati in the true sense was an act of chastity from the side of the wife. Srimad Bhagavatam, a classic Vaishnava literature documents such chastity in the form of Gandhari, the wife of Drthrashtra. Srila Prabhupada comments on this particular verse describing sati practice.
dahyamāne 'gnibhir dehe
patyuḥ patnī sahoṭaje
bahiḥ sthitā patiḿ sādhvī
tam agnim anu vekṣyati
While outside observing her husband, who will burn in the fire of mystic power along with his thatched cottage, his chaste wife will enter the fire with rapt attention.
Gāndhārī was an ideal chaste lady, a life companion of her husband, and therefore when she saw her husband burning in the fire of mystic yoga along with his cottage of leaves, she despaired. She left home after losing her one hundred sons, and in the forest she saw that her most beloved husband was also burning. Now she actually felt alone, and therefore she entered the fire of her husband and followed her husband to death. This entering of a chaste lady into the fire of her dead husband is called the satī rite, and the action is considered to be most perfect for a woman. In a later age, this satī rite became an obnoxious criminal affair because the ceremony was forced upon even an unwilling woman. In this fallen age it is not possible for any lady to follow the satī rite as chastely as it was done by Gāndhārī and others in past ages. A chaste wife like Gāndhārī would feel the separation of her husband to be more burning than actual fire. Such a lady can observe the satī rite voluntarily, and there is no criminal force by anyone. When the rite became a formality only and force was applied upon a lady to follow the principle, actually it became criminal, and therefore the ceremony was to be stopped by state law. This prophecy of Nārada Muni to Mahārāja Yudhiṣṭhira forbade him to go to his widowed aunt.