At the beginning of summer, trendy Iranian women started wearing lighter clothes, more transparent veils to cover their hair and slightly shortened sleeves that still end below the elbow.
That tendency prompted the more conservative sectors to demand imposition of "good hijab" in accordance with a much stricter interpretation of the Islamic dress code.
But the Ansar-e Hezbollah group has gone further and organised street patrols in Tehran "to control morality in women", especially young women, who are more relaxed about complying with the hijab, which requires a woman to cover everything except her face, hands and feet.
The paramilitary group, which has the support of Supreme Leader Ayatollah Ali Khamenei, claims to have trained and launched "dozens of groups to enjoin good and forbid evil".
The group's 3,000 women and 1,000 men patrol the streets in civilian clothes to warn and intimidate those women who, in their view, violate the rules of decency required by the Islamic Republic.
The secretary general of Ansar-e Hezbollah, Abdolhamid Mohtasham says it is necessary "to crush those who spread corruption".
This development comes shortly after Rouhani, who won an election after promising greater social freedom, said in a speech that behaviour cannot be imposed on people.
"Is it possible to improve culture with vans, minibuses, police and soldiers?" he asked, in a clear reference to the morality police, who also prowl the streets.
"This is a religious dictatorship," Saide, a 29-year-old resident of Tehran said.
She wears an ordinary veil similar to many young women, exposing much of her hair.
Her classmate Sharshani, 26, believes that "this act shows no respect for people".
"Each person should be able to dress as he or she wants" is an idea that has been taking hold in a country with a predominantly young population.
Fatima, who works for a tourism company, points out that "in other (Muslim) countries, such as Turkey, there are women who are veiled and some who are not".
"But those who are veiled do not look down at those who are not, they respect them, but here, they look at us with hatred, just because we wear makeup or nail polish," she said.
"In theory, we cannot expose our hair in the street. But we all show it, but that means we could be stopped at any time. Always walking in fear."
The presence on the streets of some 4,000 Islamic hardliners who do not respond to any official authority will only complicate the situation for those who have a more tolerant view of hijab.
Iranian Interior Minister Abdolreza Rahmani-Fazli said the patrols would need official authorisation to operate and made it clear that such permission would be forthcoming.
"The interior ministry is responsible for seeing to these issues and will have an appropriate response to the measures," he said.