PSNI is sued over holiday pay
More than 1,300 police officers are taking Chief Constable George Hamilton to court for holiday pay.
Officers claim they are owed money going back at least 20 years in light of a landmark court ruling in 2014.
However, the PSNI warned it could cost millions and directly impact on crime fighting in Northern Ireland.
The details were revealed by the BBC's Stephen Nolan Show.
The action is being supported by the Police Federation, which said that there was a question to be answered over whether officers were entitled to three months' backdated holiday pay or if their claims should stretch back to 1998, when new working regulations were introduced.
Retired Detective Superintendent Alan Mains said the action - if successful - could cost millions and money would have to be set aside by the PSNI until a judgment was made.
"Obviously, the officers feel they have a case. During my time, from 1978 onwards, there was an expectation that officers had to work overtime," he said.
"If there is a reward then they probably deserve it - don't forget the family time that had to be sacrificed.
"Greed doesn't come into it; if there is a requirement in law for it to be paid then it should be paid."
The action follows on the back of a court ruling in Scotland in 2014 that said people who regularly work overtime would be owed additional holiday pay. Other police officers across the UK have taken a similar action against their own forces.
Deputy Chief Constable Drew Harris said: "At a time of austerity, I must manage scarce resources prudently so as to best protect the people of Northern Ireland.
"It is perfectly understandable that officers and staff should seek to avail themselves of their entitlements in relation to overtime and holiday pay.
"However, there are difficult points of law which mean that I would be failing in my responsibilities if I didn't seek clarity in the courts, especially when the potential sums of money at stake are very large and would have direct operational impact upon policing."