The founder of one of the country's biggest property investment clubs says its 20,000 investors can't afford their mortgage repayments after the banks shifted them from interest-only loans to principal-and-interest mortgages earlier than they expected.

"How would you manage if your bank told you you had to pay 45 per cent more per month on your mortgage?" Kevin Young, founder of Queensland's Property Club (previously called The Investors Club) told The Australian Financial Review.

"We're advising our members to get themselves into conflict with their bank, to say they can't afford principal and interest repayments without ending up in financial stress. Most of the time, the bank will acquiesce," he said.

Kevin Young, pictured here with his wife Kathy, says he has been forced to sell properties. Tony Moore

Mr Young, who claims to own a portfolio of nearly 200 properties making him the country's "largest individual residential property owner", said he had been forced to sell some of his own properties due to the lending changes.

Interest-only loans typically cover a fixed period (up to five-years) and are charged at a higher interest rate, before reverting to principal-and-interest repayments for the remaining period.