Prime Minister Helen Clark says she will not reprimand her Communications Minister David Cunliffe over comments last week that saw $200 million shed from Telecom's sharemarket value.

Mr Cunliffe told financial news service Bloomberg mid-week that Telecom might have to cut dividends to fund increased investment after being forced to open its network to competitors.

Telecom's share price immediately dipped, but had fully recovered its losses by the end of the week.

Mr Cunliffe said his comments were based on publicly available information rather than anything confidential he had received as minister.

But Opposition MPs have called for Mr Cunliffe to step down while the Securities Commission investigates his comments.

Helen Clark today said she would not be reprimanding Mr Cunliffe over the comments.

"In my view David Cunliffe said nothing that numerous commentators haven't said before," she said on TVNZ's Breakfast show.

"The minister had no inside information."

She said Mr Cunliffe had merely been commenting on the well-known fact that many New Zealand companies paid out high dividends at the expense of greater investment.

"I don't think he can be held responsible for a reaction to comments which were no different from those many commentators have made over a period of time."

National's deputy finance spokesman Bill English said Helen Clark's defence of Mr Cunliffe amounted to "an endorsement of his reckless behaviour".

"It doesn't matter whether it was sinister or not, it's still stupid," he said.

"As the minister who can make decisions which could affect the share price, he simply should not be sounding off."

Mr English said the Prime Minister's claim that there was no difference between Mr Cunliffe's comments and those made by market commentators was ridiculous.

"As the Government gets more hand-on with business, this level of ignorance is dangerous," he said.

Sharemarket watchdog the Securities Commission said last week that it was investigating Mr Cunliffe's comments.

NZX, which operates and co-regulates the sharemarket, referred the comments to the commission on the grounds they affected "the transparent and orderly functioning" of the market.

The commission said it would examine whether Mr Cunliffe "could or should have taken, or refrained from taking, any actions in respect of these matters to maintain the transparent and orderly functioning of the securities markets in New Zealand or elsewhere".