Prime Minister John Key is confident the government's plain packaging policy for cigarette packets will survive any legal challenges.
Christopher Bishop, a lobbyist for tobacco company Philip Morris, told TVNZ's Q+A programme on Sunday that plain packaging will break World Trade Organisation rules by setting up a two-tier system for trademark rights.
However, it was too early to say if the company would sue the government.
Cabinet has agreed in principle to plain packaging and from next month supermarkets, dairies and other retailers will be banned from openly displaying packets of cigarettes or tobacco.
Mr Key told TVNZ's Breakfast programme on Monday tobacco companies had argued plain packaging did not work.
"If plain packaging makes no difference why do they care that we are doing it," he said.
"To the best of my knowledge we have the sovereign ability to control what is on our shelves."
He said the issue may be affecting the government in polls but the government cared about people and wanted them to live.
"Sometimes, as a government you have to step forward and stand up for what you believe in," he said.
The government wants to make New Zealand smoke-free by 2025.