Mum-and-dad shareholders in New Zealand's top listed companies are the target of a predatory offer to buy shares for much less than they are worth.

Stake owners in companies such as Telecom, Vector, Fletcher Building and Fisher & Paykel Appliances have been contacted by limited partnerships linked to Christchurch property developer Bernard Whimp.

The letters urged shareholders to sell their shares at up to 40 per cent less than they are worth on a "first come, first served" basis, encouraging them to "act now if you wish to accept".

Mr Whimp, who uses limited partnerships to get around his recently expired four-year ban as a company director, has a track record of making low offers for shares and debentures.

In August, he made offers for four million DNZ Property Fund shares, and bought 2.2 million at 60c each.

Shares in DNZ have since traded at between 99c and $1.22, so Mr Whimp would have made at least $858,000.

He has also been linked to below-par offers to investors in South Canterbury Finance and Strategic Finance.

Last year, he applied unsuccessfully to the Supreme Court for leave to appeal against a conviction for burglary and removing documents of a company in liquidation and failing to deliver them up.

His latest offers have angered investors.

"I get really angry at this sort of immoral behaviour," said one investor in an email to the Herald.

Another said: "These are ... sharks preying on the elderly or confused."

The Securities Commission said it was not illegal to make an unsolicited offer to buy investments for less than the market value, although it was against the law to mislead or deceive investors into accepting an offer.

Market commentator Brian Gaynor said people could get a higher price selling through the stock exchange.

He said that in Australia, such offers would need to disclose the current market value of the investments, and he described New Zealand's rules as lax.