The Australian Securities Exchange has overhauled the way companies are meant to disclose information to the market in a bid to stop confusion about their obligations.
It comes after several large listed companies - including David Jones, Billabong, and Spotless - were the subject last year of approaches from private equity players with highly conditional offers that were announced to the market uncertainly.
ASX chief compliance officer Kevin Lewis said the ASX's rule changes, which come into effect on May 1, are meant to give clarity about when companies should disclose information, and what type of information that should be.
"One of the most important changes is around the meaning of the world 'delay' when we talk about something happening promptly and without delay," Mr Lewis said.
"There was quite a bit of concern around those notorious ASIC infringement notices that involved delays of 60 and 90 minutes ... [but] we interpret 'delay' as meaning a deliberate postponement."
Mr Lewis said the rule changes were also meant to clarify how the ASX treats media and analyst reports - and market rumours - as evidence of a loss of "confidentiality".
ASX's review of continuous disclosure rules was put on hold last year when the corporate regulator alleged Fortescue Metals - and its billionaire head, Andrew Forrest - had contravened the Corporations Act. The alleged contraventions were in connection with public statements about agreements Fortescue had made with Chinese state-owned entities to finance and build parts of the miner's proposed Pilbara iron ore mine in Western Australia. The High Court found in the miner's favour.
The final guidance also comes after retailer David Jones last year received an unsolicited takeover bid from the mysterious EB Private Equity. News of the offer sent the retailer's share price soaring almost 20 per cent higher when DJs informed the market.
But Mr Lewis said that event had been factored into the consultation draft and it did not change the final draft.
The ASX rule changes are also meant to clarify how the ASX treats the disclosure of earnings surprises, including the role played by consensus estimates in setting market expectations of earnings.
They also clarify ASX expectations on the monitoring of social media by companies.