Nine Christians, including a church pastor, have been sentenced to five years in prison by the Iranian authorities.
Church leader Matthias Haghnejad and eight members of the Church of Iran denomination received the sentence after a short trial on September 23. They were all arrested earlier this year.
Christian Solidarity Worldwide (CSW) said it was clear from the brevity of the trial that "due process was not observed".
A source in the country told the organisation that "it seemed as if the judge had already made his decision and allowed this process as a formality before pronouncing a pre-determined sentence."
At a previous court hearing held on 24 July, CSW reports that the judge, Mohammed Moghisheh, attempted to coerce the pastor and four of the other Christians into accepting a court-appointed legal representative.
When they refused, the hearing was suspended and the men were remanded in custody with their bail terms significantly increased.
The trial of the remaining four was resumed on 28 July, when Judge Moghisheh asserted that the Bible was falsified and that the men were "apostates".
CSW said that Judge Moghisheh was "notorious for miscarriages of justice" and that the charges against the Christians were "completely unfounded".
They are all appealing their sentence.
CSW's Public Affairs Team Leader Kiri Kankhwende said: "CSW condemns in the strongest terms the sentences handed to these nine Christians.
"Once again it is clear from the brevity of the trial and reported lack of interest of the presiding judge that due process was not observed, and that the judge was not impartial.
"The charges against these Christians are excessive, completely unfounded and constitute a criminalisation of a religion which the Iranian constitution purportedly recognises.
"We call for the immediate and unconditional release of these nine men, and all who are detained on account of their religion or belief in Iran."