This is according to Bloomberg, which on Thursday reported the news, citing two people familiar with the situation.
Such a ruling from the WTO has been widely anticipated as giving a green light for other countries to roll out similar laws, not only on tobacco but also on alcohol and unhealthy foods.
The Australian law goes much further than advertising bans and graphic health warnings enforced in many other countries.
The rules, introduced in 2010, ban flashy logos and distinctive-coloured cigarette packaging in favour of drab olive packets that look more like military or prison issue, with brand names printed in small standardised fonts.
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Tobacco firms said their trademarks were being infringed, and Cuba, Honduras, Dominican Republic and Indonesia complained the rules constituted an illegal barrier to trade.
Although the WTO’s final ruling is not expected until July, a confidential draft said the laws were a legitimate health measure.