Deputy mayor and Whanganui's Labour candidate, Hamish McDouall, called the reduction a "massive cut".
"State housing ensures people who are in real need won't have to pay more than 25 per cent of their income on housing.
"Without state houses, these people will be forced into the private rental market, where they will pay higher rents and have less security of tenure."
Mr Sowry said HNZ's planned reductions were needed because the demand for houses was constantly changing.
"It's a fluid process, and we wouldn't be doing our job properly if we weren't constantly monitoring demand and planning for the future," he said.
"This is part of managing the $16 billion state housing portfolio on behalf of taxpayers. We've also been saying in our public accountability documents for a number of years that we need to reconfigure our stock.
"For example, on page 20 of our latest statement of intent, we state: 'The configuration of our houses has not kept pace with the changes that have happened in New Zealand over the last few decades. We have too many houses in provincial New Zealand where demand is lower, and not enough in major cities.'
Mr McDouall called the projection "government asset-stripping" of regional New Zealand to pay for an increase of housing stock in Auckland.
"The number of state houses in Auckland will rise by almost 3000," he said.
"It's not as if people aren't needing a decent roof over their heads in Wanganui.
"The fact is, the Government has tightened the rules so that even very poor people cannot get on the HNZ waiting lists. The result is that in almost every provincial town and city there are dozens of state houses lying empty, while needy people are forced into often substandard and overcrowded private rental housing."
Selling state houses in Wanganui's already slow real estate market would further lower property values, he said.
"Wanganui is already suffering higher mortgage interest rates and LVR minimum deposits because of the Government's failure to control the Auckland housing crisis.
Tupoho Iwi and Community Social Services Trust social worker Kataraina Shepherd thought the cut would be detrimental to the community. "It would be harder, especially for those that don't understand the system," she said.
Whanganui MP Chester Borrows disagreed with Mr McDouall's statement that needy people could not find state housing, and said it was pointless to have vacant state houses when they were needed in other parts of the country.
"They will be bought by people who couldn't normally afford to own their own home," Mr Borrows said.
"If there was an ongoing need for more houses in Wanganui, then the Government would buy more houses here.
"If he was aware of the history of state housing in Wanganui, then he would know that the houses that we made available for lower income people to purchase in the'90s was very successful.
"You don't go into a state house and stay there for life," he said.
Ministry of Social Development general manager Marama Edwards said the core policies for assessing housing needs and calculating income-related rents had not changed.