Parliament will today debate the partial sale of four state-owned energy companies, but opposition parties are promising to propose a number of amendments to hold up the law change.

The Mixed Ownership Model Bill allows for the sale of up to 49 per cent of Mighty River Power, Genesis, Solid Energy and Meridian.

Prime Minister John Key said he sensed the mood against the sale was "slightly changing".

"It's slightly improving and, over time, as people get the opportunity potentially to participate in buying shares and can see the merits of it... I think it's one of those things where there'll be an increase in public support for it."

He said three or four people approached him at Fieldays last week and said they were opposed to asset sales. But four or five hundred told him they thought he was doing a good job.

However, Labour leader David Shearer said opposition to the asset sales was growing.

Whenever he was out collecting signatures for a petition to stop asset sales, National Party voters approached and asked to sign it, he said.

"I think there's a feeling in New Zealand that this is a backwards step, that it will result in higher power prices, that it will result in our assets being owned by offshore interests and I think they've got every right to worry."

And the loyalty scheme aimed at keeping shares in New Zealand ownership may actually reduce the value of the shares because there would be more of them, he said.

There was nothing in the legislation to ensure New Zealand investors were at the front of the queue.

"The mum and dad investors, I think, is a bit of a joke. Most New Zealanders at the moment will not be able to afford to, or even think about, putting money into these companies."

Labour will put up a couple of dozen amendments to the bill and would support the Greens amendment to keep the companies under the OIA and Ombudsman.

"We're not aiming to filibuster in a ridiculous way but we will be debating this issue hard today and  we will be putting up amendments which we think will make a bad bill less bad."

The Greens were also planning to introduce a number of amendments when the bill is debated this afternoon.

- © Fairfax NZ News