Vector is warning shareholders about an Australian company making unsolicited or "low ball" offers for shares at considerably less than the market value.
Washington Securities is offering shareholders in the energy company $2 per share, nearly 30% below the $2.82 they were priced at on the stock exchange on Wednesday.
Vector chairman Michael Stiassny is urging shareholders to seek independent advice from their financial advisor.
He said the hundreds of Vector shareholders caught out in low ball share offers over the past 18 months have potentially lost hundreds of thousands of dollars collectively in the deals.
Under new rules, unsolicited share offers must be made within a concise disclosure document and shareholders can cancel any acceptance of the offer up to 10 working days after the date of the acceptance.