"These shareholders did not receive a fair price for their shares and that is just not good enough," he said.
Stiassny said he supported calls from other listed companies, for the Financial Markets Authority (FMA) to step in and legislate to stop low ball offers from being made.
"It is ridiculous that these offers continue. The sooner these are stopped the better for us all," he said.
Stiassny said the company had received a large number of calls from shareholders who have received letters from Stock and Share Trading and were concerned about the offer.
One Vector shareholder received an offer from the Australian trading company to sell for $1 a share.
At the time of the offer the shares were trading at $2.80.
Yesterday Vector shares closed on $2.85.
Accepting the offer would give the shareholder just $840 compared with the $2394 they could have been sold for yesterday on the sharemarket.
The shareholder, who asked not to be named, said she was angry at being targeted and was concerned for more vulnerable shareholders.
"It might not be illegal, but it's immoral and unethical."
She said the letter's wording and design could mislead people into thinking they would benefit from this.
"It appears to be taking advantage of a loophole in the law or regulations which should protect consumers against this kind of predatory practice. These people should be investigated by some kind of regulatory body and named and shamed, even if no criminal charges can be brought against them."
However, Stock & Share is within its legal rights to do this. There is no law preventing it from accessing a company's shareholder list and contacting those listed.
Companies like this target "mum and dad" shareholders, because they are not likely to keep track of how much the shares are trading for and may be looking for quick, easy cash.
The Financial Markets Authority, which monitors these companies, said it was doing everything it could to protect investors.
A spokesman for FMA said it was able to insist letters containing a low ball offer for shares carried a warning statement disclosing the market price of the securities and recommending that investors seek advice before accepting the offer.
"Although the FMA is unable to stop this, it can insist letters carry this."
The spokesman said the FMA had "utilised the full extent of its existing powers" under the bill.
Stock & Share this week also targeted Rural Equities investors, suggesting they sell shares at 29 per cent less than their market price.
Previously the FMA used its powers against Christchurch property developer Bernard Whimp, who had also approached investors with offers.
Last year Whimp sent letters to shareholders urging them to sell shares at up to 40 per cent less than the market price; he also insisted on a "first come, first served" basis.
The FMA replaced the Securities Commission and was given stronger powers.
Vector will send letters to shareholders warning them about the "low ball" offers.
Stiassny said he hoped shareholders would not sell shares below their market value.
Who is Stock & Share
Trading Company?
* Australian based.
* Owned by John Armour.
* Represented in New Zealand by Andrew Kennedy of Auckland law firm Prudentia Law.
