Speaking after his roundtable discussion with 12 retirees in Port Macquarie on Wednesday, Mr Turnbull said the group told him how they would fare under the proposal.

He said some sections of the group had indicated there would be a reduction of between 15 to 20 per cent in their overall incomes.

"I've just had a very good discussion with a cross section of retirees about the real hit they would take if Bill Shorten had his way and stopped them getting the franking credits benefits," he said.

"It is massive.

"One couple said it will cost them $3500 a year. That's a couple that has saved, has managed their affairs very carefully.

"They've said their private health cover will go. To lose your private health cover because of Bill Shorten; to take this off people, they are not millionaires.

"A number of people this morning made the point that this plan would encourage retirees to sell their shares and either put that money into a principle residence to qualify for a pension or a higher pension, or, they said, they will spend their nest egg and then go on the pension.

"It is a tax grab that goes after people aged over 65 years."

Mr Turnbull said the current system was sustainable with the budget showing the government coming back into surplus by 2021.

"Each year our forecasts of return to surplus have improved.

"We believe we will get there. We are confident of that. But what Shorten is doing is racking up an enormous tax grab of $200 million over 10 years.

"And Labor will just spend it. We won't get back into surplus."

He said older Australians overwhelming want to be independent and self-reliant. The Opposition plan is 'punishing them', he said.

The Prime Minister said the assertion that 'this is an attack on millionaires and the very rich is nonsense'.

"It is quite the reverse. It is not a loophole. It is a bipartisan policy from 2000, and now they (the Labor Party) want to reverse it."

Mr Turnbull said his Port Macquarie had followed an invitation from Cowper MP Luke Hartsuyker.

"How could I turn down his invitation," the Prime Minister said.

One of the attendees at Wednesday’s Port Macquarie roundtable with Prime Minister Malcolm Turnbull says he and his wife would consider their financial position under the Opposition’s plan.

“We currently have four sources of income, part pension, shares dividends, franking credits and interest,” Willie Millard said.

“The area under most threat (from the Opposition’s plan) for me personally is the franking credits, which constitutes about 17 per cent of our income at the current time.

“If this tax came in … I could lose the entire 17 per cent of my income.”

Mr Millard, from Urunga, said he had thought about a ‘what if’ scenario which would see he and his wife Odette ‘blow (spend) sufficient money that would see us on the full pension’.

“I would not have the benefits of the franking credits but I would still have my share portfolio,” he said.

“We would actually be better off.

“Taking this plan into account, where I would lose the franking credits, the full loss to the taxpayer would be $5077 a year.

“We would become an increased cost to the taxpayer.”