In December 2010 Australia changed its laws forcing share registry applicants to state the purpose of their request and gave companies the right to turn down an offer to access their share register for the purpose of making an unsolicited share offer.
The changes also prevent someone who has obtained the information from using it to make an unsolicited offer to investors.
"Australia has been through this in the past and closed the loophole," Marshall said.
But it was still open in New Zealand and that was exactly where Australian companies were now trying their luck, he said.
Stock and Share Trading, the company which has targeted Vector, Tower and a number of listed company shareholders through low ball offers, is an Australian firm.
Stan Malcolm, head of operations at Link Market Services, said it was important the public retained the right to request the shareholder register but applicants should be forced to disclose the reason why they want it.
Financial Markets Authority chief executive Sean Hughes said New Zealand's law was moving in the same direction as Australia.
The Financial Markets Conduct Bill includes a number of proposed provisions in relation to share register requests, which would give the FMA and companies grounds to decline certain requests.
Those grounds are still to be determined by Parliament, and are subject to when that bill is passed which is not expected to be until next year.