An engineer strode onstage at an event in Tehran, Iran, wearing tight pants and a stylish shirt, and clutching a microphone in one hand. Her long brown hair, tied in a ponytail, swung freely behind her, uncovered, in open defiance of Iran’s strict hijab law.

"I am Zeinab Kazempour,” she told the convention of Iran’s professional association of engineers. She condemned the group for supporting the hijab rules, and then she marched offstage, removing a scarf from around her neck and tossing it to the floor under a giant image of Iran’s supreme leader, Ayatollah Ali Khamenei.

The packed auditorium erupted in cheers, claps and whistles. A video of Kazempour went viral on social media and local news sites, making her the latest champion for many Iranians in a growing, open challenge to the hijab law.