(CNN) -- Sajjad Mohammedie Ashtiani travels to a Tabriz jail in Iran every Monday to see his mother.

And for 15 minutes each week, he speaks to his mother, Sakine Mohammedie Ashtiani, through the prison glass that divides them.

Neither mother nor son ever know if the visit will be their last.

Convicted of adultery in 2006, Ashtiani has been sentenced to be stoned to death for her alleged crime.

Originally sentenced to 99 lashes for her alleged "illicit relationship outside of marriage," Ashtiani endured that punishment in front of her then 17-year-old son.

"The authorities asked if I wanted to wait outside. I said no. I could not leave my mother alone."

Sajjad says it is a day he will never forget. But, he says, that day he thought the worst was over.

"I was thinking, OK, they hit her, now it's finished. They told me this process was finished. She's done. She's free to go. "

But then a judges' panel in Tabriz suspected Ashtiani of being involved in her husband's murder and re-opened her case.

She was cleared of the murder charges, but the panel re-examined Ashtiani's adultery sentence, and based on unspecified "judges' knowledge," decided she should be put to death for the alleged affair.

"At that time it should have been finished. They should have punished her only once," says her son. "Her documents say she is innocent. She paid for the crime five years ago."

Human rights activist Mina Ahadi, herself forced to flee a death sentence in Iran almost 30 years ago, has also taken up Ashtiani's cause, working with Sajjad and his sister Farideh to get their message out.

She says pressure from outside Iran can make a difference.

"Legally, it's all over, and we have no chance. It's a done deal. Sakine can be stoned at any minute. But we have experienced again and again that when we organize events world-wide, when we protest world-wide, and in particular when we contact European governments and these governments put pressure on the Islamic regime in Iran, sometimes we have a chance."

So far, there has been no response from Iranian officials about the Ashtiani case.

And with all legal appeals virtually exhausted, Sajjad says the Tabriz court has told him there is only one thing that can stop his mother's imminent execution.

"They told me if supreme leader Ayatollah Khamenei ... or Judiciary Chairman Sadegh Larijani grant my mother a letter of pardon, she will go free."

Sajjad says he traveled to Tehran six times to obtain that letter, but has been unable to gain an audience with either man.

But he refuses to give up. He is turning to the international community in hopes the Iranian government will hear his voice.

"It is crucial I tell these men what I have to say.

"Dear Mr. Khamenei, Mister Ahmadinejad, and Mister Larijani:

"All I ask for is a letter. I want a letter for my dear mother. Please write this letter of pardon because she is innocent, 100 percent innocent. If you do not have respect for what I am saying, just take a look at her file. You will see she is innocent.

"To the people of the world, I want to say, for this situation we are in: Help us. Whoever can tell the government to stop this, please do. If you can pressure Ayatollah Khamenei or Sadegh Larijani to give my family a letter, please get them to send it to us."

Sajjad knows he is taking a risk by speaking out so publicly, but says he is not afraid for his own safety.

"I am just fighting for what is right," he says.

"My mother is a housewife, a good person, a caring mother," Sajjad says.

And she has grown weary of what seems to be a punishment without end.

On his last visit with her she told him, "I can't stay in this prison any longer."

And so Sajjad and his sister Farideh are reaching out in any way they can to try and save their mother's life.

In their open letter to the international community circulated on websites, Facebook pages and through human rights organizations late last week their anguish is clear.

"Today we stretch out our hands to the people of the whole world," the letter reads. "It is now five years that we have lived in fear and in horror, deprived of motherly love. Is the world so cruel that it can watch this catastrophe and do nothing about it?

"We resort to the people of the world, no matter who you are and where in the world you live. Help to prevent this nightmare from becoming reality. Save our mother.

"We are unable to explain the anguish of every moment, every second of our lives. Words are unable to articulate our fear."

CNN's Ben Brumfield contributed to this report.