Josh Williamson, who leads the Craigie Reformed Baptist Church in Perth, was quoting from the Gospel of St John when he was approached by officers who told him they had received a number of complaints about the noise.
Mr Williamson, 27, said: “The officer told me to stop as I was breaking the law. I asked him what law I was breaking and he replied that I was in breach of the peace.
“When I asked him to explain, he pointed to my mp3 recorder and said I was too loud. I pointed out to the officer that I wasn’t using amplification, but just my natural voice. I then asked him what a reasonable sound level would be.
“The police officer replied that the noise level isn’t the issue, but rather that a complaint had been made.
“I tried to reason with the officer, explaining that such argumentation is subjective as anyone can claim anything is too loud. After a few more minutes I was placed in the back of a police van.”
Mr Williamson was taken to Perth police station where he was given a verbal warning and told to leave.
“It was basically, if you keep doing it, we’ll keep going through this process,” he said.
The pastor, a father of two, then returned to the St John’s shopping centre in the city to continue his sermon.
Now Mr Williamson says he has instructed his lawyer to look into taking legal action against the police for obstructing his right to freedom of speech. He said: “I wasn’t scared of this. It is not unknown that we may face challenges such as this – the Bible tells us that we should expect opposition to our beliefs.
“I met some very good people including other police officers when I was at the station.”
“It is my intention to go back to Perth city centre and I will also be part of a group preaching the gospel on Saturday, and God willing, beyond that.
“I am only using one of the freedoms of this country, to speak as I do. I am doing nothing wrong.”
He added: “I was performing a legal activity. I haven’t got a criminal record and I have absolute respect for the police.
“All I ask for is the legal right to perform my duties as a minister of religion.”
Mr Williamson is represented by barrister Andrea Williams from the Christian Legal Centre, which has fought several high- profile cases.
Lawyers from the centre acted for a nurse who complained that the NHS told her to stop wearing a crucifix on a chain, and a Christian couple embroiled in a row over foster children after a social worker raised concerns about their stance on homo-sexuality.
Ms Williams said: “We’re still in the process of considering what legal action we’ll take against Police Scotland but there are a number of avenues we can do down. It was unjustified.”
A spokeswoman for Police Scotland said: “Due a number of complaints from members of the public about the noise being made by an individual in Perth’s High Street yesterday, a man was asked to attend at Perth police station, where he was spoken to.
“He was issued with a warning.”