An increasing number of women in Iran are getting on their bicycles to protest against a fatwa banning them from cycling in public.

Hardline Iranian leaders believe women on bikes are a threat to morality and are strictly forbidden as a means of public transport.

Women must also be completely veiled, even in the height of summer, when playing sport or driving.

But a counter-movement, propelled by social media, has emerged over the last year. In a country of record-high air pollution and traffic congestion, more and more women are cycling.

Following a popular measure called “car-free Tuesdays” that started in the city of Arak two years ago, women spotted an opportunity to cycle in the name of the environment.

But the movement was cut short when a group of women cyclists were arrested in Marivan in Western Iran. They were released the same day after they signed documents, pledging not to cycle again despite no law against it.

There were then a flurry of press declaring women could cycle as long as they pertained to religious customs and the dress code.

But in September, Iran’s supreme leader, Ayatollah Ali Khamenei, issued a fatwa that women were not allowed to cycle in public.

Women subsequently posted pictures of themselves on bikes on social media with the hashtag #IranianWomenLoveCycling.

A mother and daughter filmed themselves cycling on the island of Kish, alongside posts explaining how they immediately rented two bicycles after the fatwa.

“Cycling is part of our lives. We were here when we heard Khamenei’s fatwa banning women from cycling,” they said.

Another woman posted a video and said she was “proud to resist the oppression”.

“As I believe those who oppress us are wrong,” she wrote. “Biking for women is not a taboo. And no one can tell me it is.”

Despite the fatwa, an increasing number of women cycle through the hilly and traffic-clogged city of Tehran.

A group of cyclists, including women, also gather outside the Tehran Azadi stadium on Friday mornings to race on the cycling track, The Guardian reported.

Nanaz, a 30-year-old lawyer, told the paper that she cycles up to 80 km per day.

"As long as [the moderate Hassan] Rouhani is our president, we will be able to do it. My great ambition is to take part in the Olympics," she said.

The Iranian Cycling Federation does not have even 100 members, yet male Iranian cyclists have won competitions across Asia.

Cycling used to be more common.

During the first half of the 20th century, when cars were an expensive import, many residents used their bikes. In 2017, Tehran's new bike-sharing system has reportedly had little uptake and the 2016 plan for 120 bike stations around the city has yet to be implemented.

Even in the bike-friendly city of Isfahan, with cycle paths, a rental bike scheme and encouragement from authorities, women are still not allowed to use them.

It is unclear how long the fatwa will continue, but Fariba, a 36-year-old accountant, told The Guardian she was excited to cycle.