This year, with hardliners in power, it is the harshest in years, CBS News correspondent Elizabeth Palmer reports. So much so that outraged bystanders used a cell phone to film a young woman being arrested and stuffed into a police car for so-called immodest dress.
"I won't go," she screams. "Let go, you filthy pig."
Many Iranian women remain defiant, and in the mountains north of Tehran, where the authorities don't venture, the daring do ... showing off bare ankles, lots of hair and distinctly un-Islamic hats.
Tehran women keep a weather eye on a store window as a kind of political barometer. As soon as there's a crackdown coming, the bright colors disappear and hemlines drop.
When the regime talks tough, the tough go shopping.
Palmer took a group of women to a Tehran mall to see where they draw the lines these days.
A manteau is the outer garment that has, for many, replaced the coverall chador.
"This is long — the length is good and it covers all of your body," a woman named Afsaneh explains.
But other fashions are arrestable offenses.
"You cannot wear this kind of shoes," she points to a pair of open-toed sandals. "Oh my God, yes, nail polish is forbidden."
And a dress that would be drop-dead chic at a party would be a drop-dead offense in public.
Palmer says as a Western reporter in Iran, she has to play it safe by wearing the most basic of black.
Would the Iranians wear what she does?
"Oh God. Sorry, this is ugly," one tells her.
If this seems all style and no substance, that may be the point. The new regime is betting that women battling for freedom on the fashion front will have less energy for any larger, political fight.