Over 1,000 Iranian citizens and civil activists have signed a statement protesting "four decades of oppression of Iranian women."
The signatories of the letter were sparked by the recent arrest and suspected torture of a woman for protesting against mandatory head-scarf rules.
The letter says Sepideh Rashno's "forced confessions" on state television were a continuation of the government's systematic efforts to exclude women from public spaces over the past four decades.
"We are neither criminals nor offenders, we are the ones who, seeing the bruised eye of Sepideh Rashno, not only do not step back, but we shout together that liberation is our right, and our strength is in our banding together," the letter says.
Rashno, a 28-year-old writer and artist, was arrested on June 15 after a video of her arguing with another woman who was enforcing rules on wearing a head scarf on a bus in Tehran went viral.
The other woman threatened to send the video -- which showed Rashno riding the bus without a hijab -- to the Islamic Revolutionary Guards Corps.
After she disappeared for several days, Iranian state television aired a "confession" by Rashno in a video report on July 30 where she appeared to be in a poor physical state and was reportedly rushed to hospital after the video was recorded.
The signatories of the statement also expressed their objection to the financial penalty for inappropriate hijab and what they called the monetization of freedom.
On August 29, Reshno's brother announced the first hearing of his sister's case was held.
The ISNA news agency, quoting the head of a branch of the Islamic Revolutionary Court in Tehran, said Rashno is accused of "assembly and collusion with the intention of committing a crime against the security of the country" by communicating with foreigners and through her "propaganda activity against the Islamic Republic and encouraging people to corruption and prostitution."
Recent reports show that authorities in Iran are increasingly cracking down on women deemed to be in violation of wearing the hijab, which is mandatory in public in Iran.
The hijab first became compulsory in public for Iranian women and girls over the age of 9 after the 1979 Islamic Revolution.
Many Iranian women have flouted the rule over the years in protest and pushed the boundaries of what officials say is acceptable clothing.