National Party leader Simon Bridges says more than 17,000 lifestyle blocks in Hawke's Bay could be affected by a proposed capital gains tax.
But Finance Minister Grant Robertson says no final decision have been made on the Tax Working Group's recommendations.
While the Tax Working Group has recommended an exemption to the family home when it comes to a capital gains tax, lifestyle blocks over 4500 square metres would not be exempt.
"The reality is, that's a little over half a rugby field," Bridges said. "There are 17,657 properties in Hawke's Bay alone which fit into that category.
"That figure doesn't include those who run a business from home, or who have flatmates."
He said multimillion-dollar properties in the Auckland suburb of Remuera, or Wellington's Oriental Bay, would be exempt from a capital gains tax.
"But those in the Hawke's Bay with a few sheep and some cows will be hit. Labour claims this is about fairness, but how's that fair?"
Robertson said the Government was seeking advice on the report and no final decisions on a Capital Gains Tax have been made.
He said any capital gains made up until the point a CGT is introduced will be protected, so the tax, if adopted, will apply to financial gain made on a property only after April 1, 2021.
The recommendation to not exempt properties over 4500 square metres is based on existing laws around what is considered a "main home" when selling properties under the brightline test, a tax introduced by National in 2015.
A capital gains tax only affects a property when it is sold.