The owners of Victoria's Hazelwood brown coal mine have been committed to stand trial, accused of causing air pollution during a mine fire that was later blamed for contributing to deaths.

The fire, which started in February 2014, burnt for 45 days, covering the Latrobe Valley in smoke and ash.

The Victorian Government ordered two separate inquiries into the fire and found it most likely contributed to deaths in the Latrobe Valley.

Victoria's Environment Protection Authority has charged four companies that had a stake in the mine: Australian Power Partners B.V., Hazelwood Churchill Pty Ltd, Hazelwood Pacific Pty Ltd and National Power Australia Investments Limited.

The charges allege that as a result of the fire, the atmosphere was:

noxious or poisonous or offensive to humans

noxious or poisonous or offensive to humans harmful or potentially harmful to the health, welfare, safety or property of humans

harmful or potentially harmful to the health, welfare, safety or property of humans detrimental to any beneficial use made of the atmosphere

The companies pleaded not guilty to the charges in the Latrobe Valley Magistrates' Court this morning.

The matter will return to court for a directions hearing next month.

The Victorian Workcover Authority is separately prosecuting a fifth company, Hazelwood Power Corporation, which also owns the Hazelwood power station.

Hazelwood Power Corporation has pleaded not guilty to 10 alleged workplace safety breaches.

French corporation Engie is the parent company of all five entities being prosecuted.

The charges carry maximum fines of $10 million.

That trial is set down for August 2018.