"It's the heat sticks that contain tobacco, and there's no problem that this product contains tobacco.
"The real problem is whether this product falls within the Smokefree [Environments] Act 1990," she said.
"Significantly, because of the way the Act is structured there are issues whether in fact the product is a smoking issue, and a smoking product.
"The definition of 'to smoke' means that the product needs to be ignited."
If the Ministry can prove that the product is for oral use, but not smoking, that would make it illegal under current New Zealand law.
Philip Morris is defending the charges, arguing that HEETS is a smoking product.
Witnesses will be called this afternoon.
The two charges the company faces carry a maximum penalty of $10,000.