Hell Pizza launched its Burger Pizza last Friday featuring a "medium rare burger patty" as a pizza topping. About 3,000 of the pizzas were sold.
But the chain revealed on Thursday that the burgers were actually plant-based, meatless patties by Beyond Meat.
Some people have accused the brand of deceiving or endangering customers.
"This is straight out pure deceit. There are people who have reactions to certain vegetable-based products," said one comment on Hell Pizza's Facebook page.
"Not impressed. Having a son with six allergies and intolerances I would be furious if someone decided to fool me on what I ate," another said.
Others praised the move, however, saying they'd enjoyed the result.
"Pizza was tasty, was pleasantly surprised to discover it was meat-free," one pizza-eater enthused.
"Well played! Hope this sticks around the menu for a while," said another.
Hell Pizza said the product was well-received offline, saying "customers who tried the pizza show the true public reaction better than the debate on social media".
A potential lawsuit?
The launch of the meat-free pizzas were meant to "start a conversation", said general manager Ben Cumming.
"A lot of people are instantly put off by the idea of fake meats, so we made the call to not reveal its meat-free origins... because we were so confident they'd enjoy these patties," Mr Cumming told the BBC in a statement.
One lawyer who spoke to New Zealand outlet Stuff said there was a chance Hell had breached the Fair Trading Act, which protects consumers from being misled.
"What does a reasonable consumer expect if it says burger and there's no qualifier? A reasonable consumer is going to think its meat," said marketing lawyer Rae Nield.
But Hell says their product in no way breached the Act.
"We haven't lied about the product - we rightly called the product burger patties, and customers have read into that what they will. We are very confident there is no breach of the fair trading act, and Consumer NZ agrees with us," said Mr Cumming.
"If covertly adding meat-free options onto a pizza encourages more people to be open-minded, we're happy to do that."
The chain has now updated its website to reflect that the Burger Pizza is "loaded with chunks of medium rare Beyond Meat Burger" patties.
The Beyond Burger is made from plant proteins - usually peas, mung bean and rice. It says it is made without GMOs, soy or gluten.