Ahmad Sadr Haj Seyed Javadi, a 94-year-old political activist based in Tehran, wrote in the letter published on various opposition groups' websites that the revolutionary court system in Iran is "illegal" and the orders handed down by such courts are illegitimate.
In an interview with Radio Farda on September 5, Haj Seyed Javadi said innocent men and women are held in Tehran's Evin Prison based on the verdicts made in revolutionary courts.
He said the revolution which took place 32 years ago in Iran has ended and therefore the existence of revolutionary courts no longer makes any sense.
"In my opinion, these [revolutionary courts] are institutions run by security bodies in order to get some people in trouble or to detain them," he added.
Haj Seyed Javadi said it is the security officials who open files against people, tell the judge to issue prison sentences against them, and then incarcerate them.
What such institutions issue is not a verdict, but a "big lie," he added.
The pressure on the Freedom Movement of Iran has intensified since President Mahmud Ahmadinejad took office in 2005.
In the course of the crackdown against opposition-led protests following Iran's controversial June 2009 presidential election, a number of the party's members along with their relatives were taken into custody.