Christian sect the Jehovah's Witnesses - with 64,000 active 'disciples' in Australia - are a cruel religion with no soul, according to Melbourne cultbuster Raphael Aron.

His warning comes as the federal government considers tightening the definition of a charity to prevent some cults and quasi-religions keeping their tax free status. Independent senator Nick Xenophon has renewed calls for a national cult-busting agency.

Raphael Aron. Credit:Angela Wylie

Mr Aron, a psychologist, counsellor and director of Melbourne's Cult Counselling Australia, said the Jehovah's Witnesses had a policy of "shunning" members who left or wanted to leave by cutting them off from family members who remained.

"I am still waiting for a justification for someone to be able to rip away a five or six year old child from their extended family because Mum or Dad have decided to leave the Jehovah's Witnesses," he said.