The Corrections Association says assaults on prison guards will happen more often if the Government passes laws allowing more invasive searches.
A guard suffered a fractured cheekbone a week ago, after being attacked by an inmate in Hawke's Bay prison while carrying out a strip search.
Minister of Corrections Anne Tolley says increased search powers will make prisons safer, by giving officers more opportunities to confiscate contraband.
But Corrections Association president Beven Hanlon says prisoners will not submit to some of the increased powers, which include body cavity searches.
Mr Hanlon says that will inevitably lead to more frequent and serious attacks on guards.
He says when such searches are done in the United States they often have to happen at gun point, while in New Zealand guards are not even allowed to carry pepper spray.
Mr Hanlon says a better approach would be to use scanning machines to see if a prisoner is carrying contraband internally without physically searching them.