Four companies face air pollution offences over the Hazelwood coalmine fire in 2014 that burned for 45 days in Victoria.
The coalmine fire began in February 2014 and blanketed the town of Morwell and surrounding areas with smoke and ash, leaving many residents with ongoing health problems.
Environment Protection Authority Victoria has now charged four GDF Suez-owned companies - National Power Australia Investments Ltd, Hazelwood Pacific Pty Ltd, Australian Power Partners BV and Hazelwood Churchill Pty Ltd - with three offences each under the Environment Protection Act 1970.
The EPA says the charges allege that as occupiers of the mine at the time, these companies caused pollution of the atmosphere.
Mine owner GDF Suez Australian Energy says it does not think there is any proper basis for the charges, which it will vigorously fight.
GDF said the Hazelwood Mine fire was an unprecedented event, initiated by embers from external bushfires, which led to several individual fires throughout the mine, in challenging conditions.
Worksafe Victoria laid charges against GDF last month for failing to ensure the safety of employees and the community.
In December, a re-opened Victorian inquiry into the mine fire found there was an unexpected spike in deaths in early 2014, with poor air quality caused by the fire a major contributor.
The inquiry's report into the health of Latrobe Valley residents was released in February, with 12 recommendations the board believes should be a priority for the state government.
These include funding and improving care for people with chronic diseases, especially those with related mental health conditions.