"Dr Smith has promised that 400 state houses will be sold at a discount to first home buyers. But of the 19 houses being sold in Wanganui, three of the seven tested so far have tested positive for P contamination.
"At that rate, more than 160 of the houses for sale may be contaminated."
Mr Twyford said the Government should guarantee that all houses would be tested before they were put on the market, and if any showed traces of meth that information must be included in any marketing.
He said an answer was needed as to whether all those who had bought houses under the FirstHome policy would be given the chance to have their homes tested at the expense of Housing NZ.
"The whole episode underlines what a bad joke the Government's FirstHome policy is. It was a announced as a political stunt to distract attention from the effects of LVR [loan-to-value ratio] lending restrictions on first home buyers."
The Chronicle learned that a Wanganui woman and her partner were looking at buying a house in Wembley Place but were suspicious because some of the carpet had been removed and the interior newly-painted.
The woman spent $250 on tests to see if the property had been used as a meth lab. Those tests were positive and showed slight to moderate levels of methamphetamine.
Marcus Bosch, the corporation's property services general manager, said HNZ was made aware of the issue on April 7.
"We then requested pre-emptive testing which confirmed the presence of methamphetamine in two locations in the house," he said.
On April 8 the corporation requested comprehensive testing of the property and preliminary results indicated the presence of meth at a negligible level.
Mr Bosch said on the same day the prospective purchaser was offered the opportunity to exit the sale and purchase contract they had signed.
Mr Twyford said methamphetamine contamination was a relatively serious problem for Housing NZ and in the past three years 22 properties had been refurbished and eight demolished due to P contamination.
He said the corporation did not screen tenants based on whether they have been convicted for methamphetamine possession or manufacturing previously.