Hard-liners have protested in Tehran against what they said was the flouting of the Islamic dress code that became compulsory after the 1979 revolution.
The official news agency IRNA put the number of protesters at about 4,000.
Every year thousands of women are detained or fined for not fully observing the hijab.
President Hassan Rohani asked Iran's police in October to be lenient on the hijab issue.
"Preserving public chastity, observing Islamic hijab, and moral security are strategic matters which shall not be forgotten under the pretext of economic sanctions or government change," read a statement issued by protesters.
Hossein Hashemi, governor of Tehran Province, said the demonstration was not legal since no permission was granted.
The hard-line Fars news agency said the demonstration ended after Tehran police chief Hossein Sajedinia appeared at the rally and pleaded for it to end.
Based on reporting by AFP, IRNA, and Fars