Police staff have made 29 accident compensation claims for PTSD, mental health or anxiety disorder in the last half-decade but only six have been accepted.
Police manage their own accident compensation claims through a company called Gallagher Bassett. After five years claims can be transferred to ACC.
Sixteen claims were listed for PTSD, mental health or anxiety disorder have been declined in total.
In addition, three claims have been transferred to ACC and another three are still being assessed. One further case had also been declined, but is now being assessed.
Police Association president Chris Cahill said the number of cases being declined was a concern.
"We'd want to see if there's some obvious reason why that many are being turned down and if so, is it because of some way the legislation is being looked at, rather than addressing the concerns of these officers who have suffered?"
Homicides, road accidents and child abuse cases could all have contributed to mental distress for staff, he said.
"The day to day repetition of some of these events can also add up over time, you might handle one road accident, but when you've attended multiple over several years, that has a toll over time as well."
Police national safer people manager Corrie Parnell said the decisions were underpinned by the legislation.
"Police don't make the ultimate decision, that's the complexity of a PTSD claim, fundamentally attributing that to a singular episode is often difficult to determine."
However, Mr Parnell said support for staff was still available for those who needed it.
"Often they'll be referred through their employee assistance programme [a counsellor or psychologist], for extreme cases they're a mandatory referral, sometimes cases will have a psychologist, or psychiatrists attached to them.
"They're not short journeys a lot of theses, cases they will run into a number of months."
In addition, the Police Association has set up a fund for members of the union, who still need help once they leave the police.
In addition an app called EQUIPT has been developed for current and former staff to improve wellbeing.
Accident Compensation lawyer John Miller - who represented a New Zealand soldier who won his PTSD compensation case - said others would have to go through the already stretched public health sector.
But getting ACC cover could be tough if it was not associated with a physical injury such as a shooting, Mr Miller said.
"If it's not due to a physical injury, if it's not due to sexual abuse, then it's got to be some horrific, single event, that's the problem."
Even if people could get counselling and support at work they could be reluctant to come forward.
"You can draw some parallels with sexual abuse in the workplace. One of the reasons someone doesn't come forward is it's often seen as damaging to your career."
For those in the police or defence force, a diagnosis of PTSD could be career ending so people continued to work, he said.