"When I had a closer look there was like raw chicken goo...it was next level raw," he told Newshub.
He posted on Facebook: Close up of how raw the chicken was!!!!!! Parents please check before you give to your children...THINK OF THE KIDS PLEASE..
The man also posted details of a mix up with a refund, showing a receipt for beef sliders and an error with a second receipt for chicken sliders.
A spokesman for Burger King New Zealand said the company was taking the issue seriously and had been in contact with the couple, who were regular customers.
He said the company was trying to understand what happened with the chicken, which comes into restaurants frozen/raw and is then cooked.
"Our number one priority is customers' health and food safety."
The spokesman this was the only complaint they had received about the new chicken sliders.