Hell Pizza will be reminded of its obligations under the Food Act after selling fake meat pizzas to thousands of unwitting customers.

The fast food chain sold more than 3000 of its new Burger Pizzas last month, with most customers not realising its burger-like topping was made of Beyond Meat, a plant-based meat alternative.

Hell reckoned the stunt was a great marketing ploy but some customers claimed they had been lied to - and raised concerns they may have been unwittingly exposed to allergens.

Now the Ministry for Primary Industries has stepped in, saying after several complaints it will be talking to Hell Pizza about "the importance of consumers being aware of ingredients so they can make informed decisions".

These included knowing whether there were allergens in their food. Beyond Meat's website warns that pea protein, one of the product's main components, could pose a risk for people who are allergic to peanuts.

"Peas are legumes," the website says. "People with severe allergies to legumes like peanuts should be cautious when introducing pea protein into their diet because of the possibility of a pea allergy."

Dr Bodo Lang, head of marketing at the University of Auckland, said there was a chance the stunt had also breached the Fair Trading Act, which forbids "misleading and deceptive conduct" including selling in a way that is "liable to mislead the public as to the nature ... of goods".

"If you're saying "Burger", I think the vast majority of people would say burger means hamburger and hamburger means beef," Lang said.

But despite possible breaches of the law, he thought the saga could increase sales if people felt it meant Hell was confident in the quality of its product.

"Consumers may want to experience this first hand," he said. "It's implicit that they're suggesting to you that this stuff is as good as the real thing, so me and my meatosaurus friends will give it a try."