Women are being asked to join a rolling 24-hour fast to put pressure on the British and Iranian governments for the release of jailed charity worker Nazanin Zaghari-Ratcliffe.
The campaign by the women’s rights organisation FiLiA was inspired by her husband Richard Ratcliffe’s hunger strike outside the UK's Foreign Office.
Mrs Zaghari-Ratcliffe is under house arrest in Tehran after being released from prison, but is awaiting the start of a second jail term.
Among the women taking part are political campaigner Sophie Walker and filmmaker Vaishnavi Sundar.
“Nazanin has been waiting for us for too long,” said Ms Walker, the founding leader of the UK-based Women's Equality Party.
“I’m utterly ashamed that our government has left her alone, intimidated and ill-treated for years.
“I hope that this action prompts our prime minister and foreign minister to think again, and I hope that there is some small comfort for Nazanin in knowing that her sisters stand with her.
“The power of women’s solidarity can be a comfort in the darkest times. I hope FiLiA’s campaign can bring some warmth and light to her and I am glad to join.
“She and many others are being used as pawns in geopolitical games that separate families and multiply suffering. We call on the British government to support Richard in securing Nazanin's release and to reunite Nazanin with her daughter, Gabriella.”
Mrs Zaghari-Ratclife was imprisoned in April 2016, when she visited Iran to introduce her daughter, Gabriella, to her parents.
Her husband has staged a high-profile campaign to keep the pressure on the Iranian and British governments.
Mr Ratcliffe and FiLiA said they only want people healthy enough for fasting to go without food but that other people can add pressure by writing to their MPs.
“It is deplorable that women from all walks of life have to resort to these tactics to ensure women's human rights are protected,” FiLiA spokeswoman Raquel Rosario Sanchez said.
“She and many others are being used as pawns in geopolitical games that separate families and multiply suffering.”
“We are inspired by the courage shown by Nazanin,” Ms Sanchez said.