AJM Chart, page-107

Just to clarify what Ozblue is saying there are certain requirements under corporation law that shareholders are required to do.  See http://download.asic.gov.au/media/1236706/rg5-published-20-december-2013.pdf for full details,
Put simply any person must advise any change in holding of 1% of more once he becomes a substantial holder of 5% .  This substantial holding must include any associates with other shareholders that he may have influence over in voting.
A substantial holder cannot increase their holding above 20% accept via a takeover offer!

the prime details are as follows:

These requirements apply when the votes attached to securities, in which a person and any of their associates have a relevant interest(as a proportion of
all voting shares or interests), increase above one of the following two thresholds:

• a) the 5 % substantial holding threshold—after which a person must provide substantial holding notices relating to movements above or below the threshold, and any change of 1% or more ( Pt 6 C.1) ; and
• b) the 20% takeover threshold—after which acquisitions and offers to acquire relevant interests in voting shares or interests are only permitted

through certain transactions or in certain circumstances ( Ch 6).

Takeovers
Acquisitions of a relevant interest in voting shares or interests that increase a person’s voting power to more than 20%, or from a point above 20%, are prohibited under s606 unless they are made under a takeover bid, authorised under one of the other exceptions in s611, or the person’s voting power is already above 90%.
This prohibition also applies to:
Ÿacquiring legal or equitable interests that result in another person’s voting power increasing in the same way; and
Ÿoffers or invitations that would result in a breach of s606 if accepted.