Pastor Yousef Nadarkhani (pictured above and below), Mohammadreza Omidi, Yasser Mossayebzadeh and Saheb Fadaie were each sentenced to ten years behind bars for "acting against national security".
Pastor Nadarkhani and Mr Omidi was also given extra two year sentences, to be served in the south of the country - ranked eighth on the Open Doors World Watch List of nations where being a Christian is hardest.
CSW's Chief Executive Mervyn Thomas said: "We are deeply disappointed by these excessive sentences, which are based on spurious charges and are clearly part of an intensified campaign of judicial harassment aimed at intimidating members of minority faiths."
Judge Ahmadzadeh at Iran's 26th Chamber of the Revolutionary Tribunal accused the men's church of receiving £500,000 per year from the British government.
They were arrested on 13th May 2016 during raids on Christian homes in Rasht - the capital of north-eastern Gilan province - by security service agents.
A ruling was expected before Iranian New Year celebrations on 21st March; however the process was delayed when the case was referred to judicial authorities in Tehran. The four men have 20 days to launch an appeal.
Meanwhile, Mr Omidi, Mr Mossayebzadeh and Mr Fadaie are still awaiting a decision on an appeal against sentences of 80 lashes each for drinking wine during a Communion service.
Mervyn Thomas added: "We urge members of the international community to extend the sanctions still in place against Iranian individuals to include members of the judiciary who are implicated in ongoing and severe harassment and persecution of religious minority communities."