New Zealand's largest tobacco manufacturer will be investigated for giving free cigarettes to its staff.

Imperial Tobacco's commercial boss Brendan Walker this week confirmed cigarettes were available to office staff and workers during breaks at its Petone factory, the Herald on Sunday reports.

"It's purely for research," he told the newspaper.

"The fact of the matter is we're keen to receive the feedback and comments on those particular manufacturing runs."

Smokefree legislation bans manufacturers from distributing tobacco products free or at a reduced charge.

However, Mr Walker says he is confident Imperial Tobacco is acting within the law as employees could choose whether to test products.

"It's entirely up to an individual whether they see it as a perk or not."

He said there were no health warnings on the products.

Hutt Valley Regional Public Health smokefree officer Kristen Foley said he would seek discussions with the company bosses next week about the test products.

Last week Imperial Tobacco officially completed a $45 million upgrade to its Petone factory which will quadruple its exports to Australia.

More than three billion cigarettes and 700 tonnes of roll-your-own tobacco will be manufactured at the plant and exported to Australia each year.

About 250 people work at the factory.