But Mr Treen, who has written a letter to police top brass about their involvement in recent McDonald's protests, stood by his comments.
"I think he is the one who should be apologising," Mr Treen said.
He cited reported comments in 2007 from then National Party police spokesman Chester Borrows, who criticised such deals saying police ran the risk of their integrity being compromised.
Police Minister Anne Tolley yesterday told the Otago Daily Times the matter was "desperate attention-seeking from a union".
"The police are out there doing their best to ensure the safety of the public, workers and union members equally."
A McDonald's spokeswoman said there was no blanket policy on discounts.
"Eighty per cent of McDonald's restaurants are owned and operated by local men and women and, yes, we understand that some franchisees elect to offer a discount on meals for their local police, fire and ambulance services.
"This discount ranges from 10 to 50 per cent and is at their own discretion."
Mr Treen said discounts led to a "culture of expectation" within police, and some Unite Union members had been berated by officers for offering a 10 per cent discount, as opposed to other outlets which offered up to 50 per cent.
"It is inappropriate to have that and especially during a period like now where police are being called every time we have a picket to provide, in my view, private security for this company."
However Mr Nicholls said "the Unite Union are trying to draw some dots that simply don't exist".
"It is almost Alice in Wonderland to try and draw a line between those officers working at the Unite protest and the discount ..."
Police policy is that a gratuity or discount is to be declined by a police employee when offered simply because they are a police employee.
However, it could be accepted if it was offered to them because they are a member of a group or organisation other than the NZ Police, such as the New Zealand Police Association.
Association vice president Stuart Mills said the union used bulk-buying power to negotiate discounts and special offers on various goods and services for their more than 11,000 sworn and non-sworn members.
"Suppliers aren't giving [discounts] to members of police but are giving to members of the Police Association, so you have to be a member of the association to access a discount card."
McDonald's was not one of the companies offering discounts for union members, he said.
New Zealand Fire Service Director of Human Resources Janine Hearn said the organisation did not pass on offers of discounted goods or services to staff unless there was already a contract for supply in place.
"Any offer must apply to all staff and cannot be part of any contract negotiations. We have only one contracted supplier listed who has offered a discount to staff, and that is a car rental company.
"We are aware that discount offers are made to staff via their unions ... we have no concerns about these discount offers."
St John South Island spokesman Ian Henderson, of Christchurch, said the organisation had no set policy around discounted goods and services.
"There are instances where St John ambulance officers in their uniform ... may get a discount but it is purely at the discretion of the store or that owner, but not something we look for."
