Police officers in Northern Ireland are working "flat-out to keep the service ticking over", it has been claimed.
The PSNI has become reliant on staff goodwill and unpaid overtime, the union representing rank and file officers said.
More than 90% of officers surveyed by the Police Federation said they were dealing with police-related matters on their days off.
It has led to warnings that falling numbers and budget constraints have left the current policing model unsustainable.
DUP MP Ian Paisley said more than 700 more police officers were needed to relieve the "unacceptable strain on policing".
Federation chairman Mark Lindsay said officers were suffering as the PSNI comes under immense pressure to "square the budget circle".
"The PSNI is under-resourced and under-staffed," he said.
"The consequence of this is that officers are working flat-out to keep the service ticking over. Indeed, over 90% said that even when they're off-duty, they're answering calls on police-related matters.
"This highlights the level to which policing in Northern Ireland has become reliant on the goodwill of officers."
Mr Lindsay said the service is operating at least 700 officers short of what it should be.
An online survey conducted by the Police Federation for Northern Ireland over a three-month period found:
- Nearly every officer routinely works paid or unpaid overtime;
- Six out of 10 officers surveyed had to rearrange childcare as a result of working overtime;
- On average officers worked almost one day of unpaid overtime each month;
- Overtime working forced eight out of 10 to cancel or miss an appointment, while almost 90% missed a family or social event because of overtime;
- Two-fifths of officers worked most, if not all, of their daily rest breaks;
- Over a fifth got less than eight hours' sleep as a direct result of working overtime more than 20 times in the three-month period.
Mr Lindsay said officers' personal lives had been "turned upside down".
"Family life is severely disrupted," he added.
"Plans are turned upside down and this causes disappointment and upset and puts family relationships under severe strain.
"As an unwelcome consequence, there is a rise in long-term sickness levels.
"In turn, that places even more pressure on officers to plug gaping holes in the service.
"Reducing budgets and diminishing resources are the main causes for this degree of upheaval.
"All officers, from the constable to the chief constable, have undoubted commitment to effective policing, but there are limits to the service that can be provided under these conditions."
Mr Lindsay urged the Executive to take action, saying the current policing model was unsustainable.
"Ministers in the Executive must realise that service levels will deteriorate or fall short of what people have a right to expect if the budget continues to be attacked, and if the issues highlighted in this survey are not addressed as a matter of urgency," he added.
"They need to carefully think what they are doing, and what they want officers to deliver.
"We were operating with 700 fewer officers than we should have to meet a peacetime policing requirement.
"On top of this, we have 30 officers leaving every month and not being replaced, which should be a cause of great concern.
"The current policing model is unsustainable."
Jude Helliker, head of Human Resources at the PSNI said: "We take the welfare of our officers and staff extremely seriously and we welcome this Police Federation survey as a further opportunity to highlight the work that members of the Police Service deliver on a daily basis to keep people safe.
"Earlier this year, PSNI commissioned a service-wide engagement and well-being survey of our officers and staff.
"Since then, we have established a working group to address issues, specifically including how we manage officer overtime and dealing with leave requests and rest days.
"We are mindful that unplanned overtime and cancelled rest days are issues that can affect personal lives and work/life balance and in recent weeks we have implemented a number of new measures to ensure that officers and staff are able to plan their work and personal lives better. We will continue to work closely with the Police Federation on a day to day basis to address both their concerns and those of their members and this survey will help us focus those discussions even further.
"Despite the various ongoing challenges that we face, our officers continue to go the extra mile every day, working with communities and partners to deliver a policing service to Keep People Safe.
"Policing is a vocation and one which is challenging but ultimately rewarding for those who have a passion for serving their communities."
DUP MP Ian Paisley said the statement "proves the breaking point at which the PSNI is operating at".
"Frankly, this cannot continue," he said.
"Northern Ireland requires at least 700 more police officers to meet the needs and requirements of modern policing.
"The ongoing pressure of policing the past and under-resourcing is catching up fast with the policing requirements. The sooner this matter of recruitment is addressed the better.
"I understand officers are quitting the service at an unprecedented number each month, and coupled with a 700 shortfall of officers this is an unacceptable strain on policing.
"I call on the NIO to urgently review policing numbers and to enter immediate discussions with the Justice Minister and the Chief Constable about rectifying this matter."