General duties constable numbers in the Southern district have fallen from 295 in 2009 to 220 now - a drop of 25.4%, figures released under the Official Information Act show.
Labour police spokesman Kelvin Davis, who obtained the figures, says police are being forced to do more with fewer resources.
The Government and Southern police have rubbished the claims and say the only thing that has changed is how police are organised.
But Police Association president Greg O'Connor says police are being forced to prioritise callouts as first responders become increasingly stretched.
General duties constables are responsible for frontline response policing and are charged with maintaining public order and safety.
Mr O'Connor said the decline in general duties constables resulted from a structural change which was first trialled in Counties Manukau district in 2010 and focused on prevention policing.
An additional 300 officers were deployed to the district to support the change in structure and focus.
''That model has been basically templated across the rest of the country without any additional resources and therein lies the problem,'' he said.
''The response staff that are left are the ones really feeling the pinch. They are the ones unable to attend the calls for service.
''We are increasingly hearing about police being late or not attending or reprioritising jobs.''
The association was supportive of the prevention policing model but it required more officers to be deployed, he said.
''It's a great idea but like every great idea it will flounder with the lack of proper resourcing - the kind of resourcing Counties Manukau got.''
Twelve of New Zealand's 13 policing districts have experienced drops in general duties constable numbers since 2009 with only Counties Manukau showing an increase. Nationally, general duties constables have fallen by 17.9%.
Data from Statistics New Zealand shows only about 50% of recorded crimes were resolved in the Southern district last year despite recorded crimes being at a record low.
Otago coastal police were recently restructured with Mosgiel's CIB disestablished and in January last year police were unable to respond to a 111 call reporting dozens of shots being fired in a residential area in Waipori because no officers were available.
''That's the sort of thing that happens,'' Mr O'Connor said.
''Everybody is reprioritising all the time and hoping like hell that the job they are reprioritising isn't the one that results in someone being hurt or worse.''
Mr Davis said the figures' revelation was a ''terrible indictment'' on the Government.
''The number of constables on the beat has fallen over the past six years in all but one of the country's 12 police districts.''
National ''talks the talk on police numbers but has allowed the number of constables handling crime and complaints to fall year after year'', he said.
''Police say they want a higher presence in New Zealand communities, yet there is no money or staff to increase foot patrols.''
Police Minister Michael Woodhouse said, in an emailed statement, Mr Davis was ''being tricky or is utterly confused'' and his comments were untrue.
''The simple fact is that both frontline and overall police numbers have increased under the National led Government, and our communities are safer as a result,'' the minister's statement said.
''There are now more police on the beat, and more foot patrols, than ever before.''
Acting Southern district commander Detective Inspector Tim Anderson said, in an emailed response, the decline in constable numbers was ''just a change in the job titles and the focus of some frontline roles''.
''There has been absolutely no reduction in police numbers `on the beat' in Southern district,'' he said.
''As the face of modern policing has changed, a number of specialist frontline teams have been created in addition to general duties staff.
''The new frontline response role titles include neighbourhood policing teams, prevention, child protection and adult sexual assault, alcohol staff, youth and family teams, etc.''
Police did not provide responses to questions about whether Otago coastal area's restructuring was linked to the decline in general duties constables or if service levels had been affected.
Mr O'Connor said police managers were forced to put an optimistic spin on the numbers because if they ''report the true situation ... they will earn political ire''.
''To say the numbers on the beat are the same is technically correct, but it's not correct to say there's the same numbers available for jobs as they arise.
''The problem police have got [is] there's been a huge increase in the number of calls for service at the same time,'' he said.
