The Prime Minister has admitted his sister-in-law works for a tobacco company but says he has not discussed tobacco policy with her.

It comes as the government faces more pressure over its connection with the tobacco industry.

On Thursday, RNZ revealed Associate Health Minister Casey Costello sent notes to health officials on reforming smoke free laws and freezing excise tax on tobacco.

But Costello doubled down on comments that she did not write notes asking for information on pausing excise tax on tobacco products

There was a line in a document last year about removing excise tax for three years, but she did not know who collated it.

It has sparked calls from health experts for the coalition government to disclose any tobacco industry links it has and for calls from the Labour Party for Costello to be sacked.

In a statement, Prime Minister Christopher Luxon said the Cabinet Office was aware of his sister-in-law's connection.

"Yes, my sister-in-law works for a tobacco company. I have never discussed tobacco policy with her."

Luxon said he was confident he has complied with the Cabinet Manual.