The militant construction union has been fined more than $55,000 for threatening "war" over a spat with building group John Holland at the Mitcham train station upgrade.

Federal Court Justice Christopher Jessup on Wednesday morning ordered the Construction, Forestry, Mining and Energy Union pay fines of $22,500 and $26,250, and organiser Joseph Myles fines of $3000 and $3375, for threatening and organising work disruption at the Mitcham rail station upgrade in August 2013.

CFMEU has been fined for threatening to go to war against building company John Holland. Credit:Peter Braig

The court said the action was an attempt to coerce the builder into complying with the lawful request that it engage a union delegate at the site.

Tensions have flared in recent years between John Holland and Victoria's CFMEU amid claims the company has attempted to lock out the union from infrastructure projects including the West Gate Bridge upgrade, EastLink and grade separations.