Iranian national Nasser Navard Goltape, and Yusif Farhadov, Eldar Gurbanov and Bahram Nasibov from the Republic of Azerbaijan were arrested on 24th June 2016, after traveling to Tehran to visit their Christian friends.
They were released on bail from Evin Prison more than four months later, with the Azeri men returning to their home country.
Mansour Borji, advocacy director of Article 18, an organisation that defends persecuted Christians in the Shia Muslim majority country said: "This recent verdict by Iran's revolutionary court is particularly alarming, as many other Iranian Christians are still awaiting trial for exercising their right to worship as Christians in privacy of their homes."
According to records compiled by Article 18, in the last three months Judge Ahmadzadeh has sentenced at least 16 Christians to between five and 10 years imprisonment.
CSW's chief executive Mervyn Thomas also voiced his concerns and said: "The charges and sentences against these four men are unwarranted and unjustifiable, given the paucity of the evidence against them."
The charity said it was particularly worried about Iranian national Goltape who unlike the three Azeri Christians who may forfeit bail by not returning to Iran, doesn't have that option.
Thomas added that the sentence was "clearly issued on a punitive rather than on a legal basis" and said: "The constant harassment of members of the Christian community ought not to be occurring in a country where the constitution not only recognises Christianity, but also states that no-one should be molested or taken to task simply for holding a religious belief.
"As the three men launch their appeal, we urge the Iranian authorities to ensure due process is observed. We also call on the Iranian authorities to take steps to ensure that the nation's practices, legal procedures and provisions come into alignment with its international commitment to ensure freedom of religion or belief for all of its religious communities."