"We've found properties from Auckland to Invercargill that are being marketed to offshore speculators. There is no benefit to New Zealand in selling our homes to speculators who have no intention of living here.
"That can only increase demand and help drive up prices."
However, Mr Martin estimated the number of offshore investors in the Western Bay would be very small and Labour's policy would not have an effect on the market. Foreign investors tended to be Australian, Chinese, English and South African immigrants who moved into the area. Sales for Mount Maunganui and Papamoa show the number of houses sold in June rose to 81 compared to 79 in June 2012. The median property price dropped slightly, from $416,000 to $410,000. Tauranga prices rose from $342,500 to $345,000, with houses sold dropping from 132 to 125.
The Labour policy is drawing mixed political reaction and has been labelled anti-Chinese.
Prime Minister John Key said there was a limited number of foreign home buyers and Labour's policy would have little impact on the market. "The reality is that not that many people come in and buy properties that aren't either permanent residents or aren't going to take up personal residencies."
Housing Minister Nick Smith said Labour was putting the blame for the housing shortage on foreigners.
"[It's] the oldest trick in the political book. There's no evidence that overseas buyers are having any discernable effect over house prices."
New Zealand First and the Green Party were backing the proposal.
There was also concern the policy would not fit with the free trade agreement with China.
Constitutional lawyer Stephen Franks said the policy was a breach of the agreement, which stated Chinese investors must be treated no less favourably than investors of any other country.