In Islam, the veil, or hijab, is an act of modesty and religious expression for women. Because of the variety of different sects of Islam, there are varying degrees of hijabs and hijab-wearers. Some women choose not to wear the hijab at all, while some women wear entire body coverings with only their eyes visible.
The Iranian state, however, has legislated and restricted the choices of these women. In 1936, for a period, the hijab was outlawed altogether in an attempt to Westernize the country. For many, however, the hijab was a deliberate action of religious expression, and forcing them not to wear it was tantamount to religious persecution (for a much less severe example, but understandable by a predominantly Christian audience, imagine if displaying crosses of any form—on a necklace, tattoo, or article of clothing—was outlawed altogether).
In later years, however, after the revolution, it was decreed that women wear full body coverings. So the choice of women to wear hijabs or similar attire has frequently been restricted and legislated by the state of Iran.