Lobby group Family First has been cautioned for using the Smokefree logo in a anti-cannabis advertisement.
The full-page ad appeared in the Herald on Sunday at the weekend and shows a hand with the Smokefree logo pulling a cigarette from a teen's mouth and another hand replacing it with a joint.
But the Health Promotion Agency says it didn't condone the use of its logo.
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An agency spokesperson said they'd be talking to Family First about the "unauthorised use" of its logo.
National director of Family First, Bob McCoskrie, said they would remove the logo if "we legally have to".
"We thought they'd appreciate the free plug."
The New Zealand cannabis referendum will be held on September 19 at the same time as the general election.
The Government released the draft Cannabis Legalisation and Control Bill last year which specifies a minimum age of 20 to use or purchase a recreational cannabis product, prohibits the consumption of cannabis in public spaces and limits use to private homes and licensed premises.