Iranian state media quote the police as saying that in the past few days, they have closed down 25 Internet cafes and given warnings to 170 cafe owners for "using immoral computer games and storing obscene photos," and for the presence of women without "proper hijab" on the premises.
At least 23 people -- including several women -- have been detained for similar reasons.
The owner of one of the Tehran Internet cafes that was inspected and temporarily closed down by police, who gave his name as Hessam, told RFE/RL's Radio Farda that police started questioning him when they found some family photos -- with a female member of the family among them -- on a computer.
"We had a few family photos in our system. They asked, 'Who is this girl that is sitting close to you?'" Hessam said. "Just because of those private photos, they closed this place for three or four days. [The police pressure] has reached that level! It has become a headache, a problem for everybody. We don't know what to do."
The Internet, and Internet cafes, have become increasingly popular in Tehran and other Iranian cities in recent years.
According to official state figures, 60 percent of the country's population has access to the Internet. However, independent sources say that figure is exaggerated, given the fact that many Iranians villages do not even have electricity. International estimates say that some 20 percent of Iranians have access to the Internet.
Most of the customers at Internet cafes are young people who come to play computer games, check their e-mail, or take part in website chat rooms and blogs.
Some Iranian journalists describe the latest campaign as an attempt by the authorities to limit access to a major source of alternative news and information and restrict Iranian's intellectual and social freedom.
Badrolsadat Mofeedi, an independent journalist and a campaigner for media rights, told RFE/RL from Tehran that the latest assault on Internet cafes is no surprise. Mofeedi said that "in addition to a crackdown on independent media, every now and then the Iranian authorities put pressure on all other sources of news and information, such as satellite dishes, the Internet, and even bookshops."
In October, several Tehran bookstores were given a 72-hour ultimatum to close down coffee shops that were operating inside their stores. Amaken-e Omomi, a state body that controls retail trade, said that operating a cafe inside a bookshop is an "illegal mixture" of trades.
"Some Internet sites have been filtered. A variety of measures has been taken to restrict the political and social atmosphere for those who are involved in the distribution of the information," Mofeedi said.
The Iranian authorities say they have blocked access to "immoral websites" such as pornographic sites.
According to Iranian independent journalists, however, many political websites -- including personal weblogs or blogs -- and many independent news sources are blocked with a filter so that Iranians cannot access them. Those sites includes radiofarda.com.
Hassem, the Internet-cafe owner, says the "heavy filtering of the websites has slowed down the Internet in Iran, reducing its speed by almost 50 percent."
The clampdown has coincided with the ongoing police campaign against anyone who violates a strict Islamic dress code.
The police have even installed mobile stations on Tehran's busiest streets to stop women who disobey the dress code, for instance by wearing a hat instead of a head scarf or by tucking their pants inside of their boots.
Isa Saharkhiz, an independent journalist and a member of the Association for Press Freedom in Iran, told RFE/RL from Tehran that enforcing these restrictions -- on everything from dress to the Internet -- has been part of the Iranian government's policy since President Mahmud Ahmadinejad came to power in 2005.
Saharkhiz said the closure of the cafes was partially aimed at preventing young people and intellectuals from getting together, as well as trying to restrict the free flow of information.
"None of these practices brought any results in the past," Saharkhiz says. "No one is able to put barriers on news and information and, especially, no one can shut down the Internet -- in Iran or elsewhere in the world."
Cafe owner Hassem said that no matter how hard the authorities try to block access to websites, young Iranians will succeed in circumventing the filter and find their way to the prohibited sites.
(RFE/RL's Radio Farda correspondent Sariborz Soroosh contributed to this report.)