A PRE-EMPTIVE strike by competition chief Graeme Samuel has put a potential kink in the $2-billion-plus float plans for share registry group Link Market Services, and the profit ambitions of stockbroker Austock.

The Australian Competition and Consumer Commission has given a clear indication it plans to oppose Link's $40 million buy-out of the third-ranked operator in the local market, Registries Ltd.

The competition commission is concerned that if the deal goes through the duopoly in the market will be too cosy, with Link or industry gorilla Computershare effectively the only choice for customers.

''The ACCC's preliminary view is that the proposed acquisition is likely to have the effect of substantially lessening competition in the market,'' said the commission paper sent to industry participants for comment.

''The proposed acquisition would remove a significant third player, that has the potential to disrupt co-ordinated behaviour … The competitive threat from the remaining small firms will likely be weak and there is limited prospect of new entry.

''Such a market structure is conducive to co-ordinated conduct, for example through customer allocation. Link and Computershare would each have little to gain from aggressively pursuing market share.''

It is believed Link, and its Sydney-based leveraged buy-out owner, Pacific Equity Partners, are outraged by the decision and will contest it vigorously.

Share registrars occupy unique positions in listed companies because they maintain the lists of a company's investors, and organise all mail-outs and meetings - effectively controlling the communications channels with shareholders.

The costs of the computer technology are high, which the ACCC argues means the cost to a company of ''switching'', particularly one with lots of shareholders, is often too high to justify a change.

Registries Ltd, the operating arm of the company Newreg Pty Ltd, is seen as an aggressive operator in the market, which has some plum corporate customers including retailer Harvey Norman, Seven Network and poker machine giant Aristocrat.