Seven human rights groups including Amnesty International have urged Iran to set aside a prison sentence for women's rights activist Delaram Ali.
Dozens of journalists and human rights activists have been detained or given jail sentences in recent months, accused of acting against the state.
Delaram Ali was sentenced to a flogging and two-and-a-half years in prison.
She was part of a demonstration last year calling for greater rights for women in Iran's Islamic legal system.
The 24-year-old says the security forces broke her left hand when they beat up the demonstrators.
Delaram Ali has been free while awaiting the result of an appeal.
But she has now been told to give herself up by Saturday so the sentence can be implemented.
She says she has not been allowed to file a complaint against the police.
Instead an internal inquiry recently exonerated the police even though foreign journalists witnessed them beating the women who were singing feminist songs while sitting peacefully on the grass in a public square.
What is notable about Delaram Ali is that she is not a well-known leader of Iran's feminist movement who has repeatedly challenged the government.
The BBC 's Frances Harrison says her punishment will be a chilling warning to anyone thinking of dabbling with politics.
And it comes as the Iranian Writers Association has talked of the increasing suppression of the press - with writers, journalists, academics, labour and social activists being arrested and newspapers closed down one after another.
One of Iran's most outspoken human rights activists, Emadeddin Baghi, was arrested last month and there has been no news of him since.
He was a man who tirelessly campaigned for the rights of political prisoners - only to become one himself, our correspondent says.
Courts have also recently upheld jail sentences for the leaders of Iran's bus drivers' union and teachers' organisations after protests over low pay.