He said performance-based pay had been unsuccessfully tried for 11 years before being ditched in 2003.
Mr O'Connor, updating members on the negotiations, said the proposed changes would place most staff in the middle of new pay bands.
"They state that police staff in bands A to D as well as constables are overpaid by as much as 20 per cent."
He warned that police bosses wanted to use three years' worth of funding to buy conditions off existing members.
This would generate savings when new constables were employed on lower pay from 2015.
Existing staff could see their pay frozen on 2015 rates "for 10 years or more", while time-in-lieu thresholds would be increased, he said.
"The Police Association is not prepared to trade ... We aren't prepared to sell out our future members," Mr O'Connor wrote.
Last night, a spokeswoman for police national headquarters said the offer outlined in Mr O'Connor's correspondence was inaccurate.
"However, in the spirit of good-faith bargaining, police are unable to publicly clarify further at this stage."
A spokesman for Police Minister Anne Tolley said it would be inappropriate for her to comment on the ongoing negotiations.
But Labour's police spokesman, Kris Faafoi, said the email revealed frontline officers were "the latest casualty in National's botched Budget".
"[The Government] is trying to lay the blame for any frontline cutbacks on police officers, when it is the Government that has failed to make the hard decisions," Mr Faafoi said.
"The Government attempted to play down police budget cuts, claiming the only significant change would be the loss of 125 sworn staff, but now the chickens have come home to roost."
