Apart from some exceptions where the issue is predetermined (Takeover bids, 4c, profit guidance, etc), the company makes the primary determination and marks the announcement as price sensitive or not - as shown below.
The ASX can however alter this: In their FAQs; Q9 & Q10:
Q9: What if I indicate the announcement is ‘market sensitive’ and ASX releases the announcement as ‘nonsensitive’? Q10: What if I indicate the announcement is not ‘market sensitive’ and ASX releases the announcement as ‘market sensitive’?
Answer (from the ASX): "The information provided by a listed entity is an indication only. ASX will make the final determination on the market sensitivity of the submitted announcement. ... Listed entities that repeatedly do this may be contacted by ASX to discuss the reasons for this.."
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