Clerics from faiths previously lambasted by Pastor James McConnell have slammed the decision to prosecute him over a fiery sermon.
A Muslim imam has vowed to go to jail with the pastor if he is convicted, while a Catholic priest branded the court case "absurd".
Pastor McConnell (78), who retired from Whitewell Tabernacle last year, is preparing to answer charges in court under the 2003 Communications Act on August 6.
The charges centre on a sermon he gave at the north Belfast Tabernacle in which he said: "Islam is heathen, Islam is satanic, Islam is a doctrine spawned in hell". It was streamed on the internet.
The pastor says despite his advanced years and his ill health, he is prepared to go to jail rather than withdraw his remarks.
"I have no regrets about what I said. I do not hate Muslims but I denounce Islam as a doctrine and I make no apologies for that. I will be pleading 'not guilty' when I stand in the dock in August."
The 78-year-old faces up to six months behind bars if convicted.
Now a prominent London Muslim academic and clergyman has vowed to go to jail with the pastor.
Dr Al-Hussaini, a Senior Fellow in Islamic Studies at the Westminster Institute, said he has "grave concerns" about the prosecution of Pastor McConnell, adding he "strongly upholds the moral right" for people of all faiths to debate.
He said: "Against the flaming backdrop of torched Christian churches, bloody executions and massacres of faith minorities in the Middle East and elsewhere, it is therefore a matter of utmost concern that, in this country, we discharge our common duty steadfastly to defend the freedom of citizens to discuss, debate and critique religious ideas and beliefs - restricting only speech which incites to physical violence against others," he said.
"All honest seekers of God's truth are enjoined to inquire, question and challenge the teachings of religious authority, and to speak prophetically to establishment power even when it means overturning the tables in the Temple.
"Moreover, in a free and democratic society, we enter into severe peril when we start to confuse what we perhaps ought or ought not to say, with what in law we are allowed to, or not allowed to say.
"While those of us who hold clerical office as Christian pastors and priests, Jewish rabbis or Muslim imams, should rightly have due care and regard to the leadership role we exercise when we make public speeches, nevertheless our foremost duty remains to express theological ideas in good conscience before God.
"For these reasons, I strongly uphold the moral right of Pastor McConnell and myself, as Christian and Muslim, to disagree about matters of doctrine and belief, and further I express my deep dismay that my fellow citizen is being subject to criminal proceedings, when at no time have any of the statements he has made incited to physical harm or hatred against anyone.
"I therefore wish to place on the record my deep concern and opposition to the criminalising of theological disagreement, at a time when our society should in fact be fostering better quality disagreement and, in that spirit, I further undertake that if Pastor McConnell is convicted and sent to prison, I shall go to prison with him."