If the Government plans on extending the brightline test as a way to substitute the Capital Gains Tax, Heather du Plessis-Allan says that there are two major flaws with the plan.
ACT has accused the Government of planning to introduce a capital gains tax by stealth.
Finance Minister Grant Robertson has asked Treasury to look at a range of tax options - including extending the bright line test.
The test has a number of exceptions - but means someone who sells a residential home within five years of its purchase must pay tax.
ACT Party leader David Seymour has raised an eyebrow at the development - as Jacinda Ardern's ruled out a capital gains tax while she's Prime Minister.
However, Robertson says the test was brought in by National, extended by Labour, and they're looking at how it works.
He says people are getting well ahead of themselves.
The suggested plan had du Plessis-Allan up in arms today. She dismissed the plan as being effective, as anyone flipping houses quickly would already be hit by the brightline test, while longterm investors generally hold on to their properties for a considerable length anyway.
She also described the plans as "incredibly dishonest".
"They made the point adnauseam there would be no more taxes. For them to extend the brightline test so it becomes a proxy Capital Gains Tax is unbelievably dishonest."