Redflex Holdings is being sued for more than $US300 million by the City of Chicago over claims its US traffic camera business bribed local officials in exchange for contracts.
The city had previously launched legal action against Redflex Traffic Systems Inc (RTSI), the US arm of the Melbourne-based company.
But on Tuesday, Reflex Holdings said it was also being sued.
"Both the company and RTSI will, in defending this legal action, make use of all available legal defences," Redflex Holdings said in a statement on Tuesday.
The City of Chicago is claiming $US377 million ($A520.32 million) in civil damages against Redflex, treble the amount the City alleges it paid to RTSI under the now terminated red-light camera contracts.
The City also wants compensation for alleged damages as well as restitution and disgorgement of alleged ill-gotten profits.
RTSI became embroiled in a corruption scandal in 2014 amid allegations it paid hundreds of thousands of dollars to John Bills, the former managing deputy commissioner of Chicago's transportation department, in exchange for him approving $US124 million in red light traffic contracts.
Bills is due to stand trial on fraud, bribery, tax, and extortion charges in January.
RTSI's former chief executive Karen Finley pleaded guilty to paying $US2 million in bribes during a Chicago court hearing in August.
She is due to be sentenced on February 18 and faces a maximum five years in jail and fines of up to $US250,000.
One of RTSI's former top salesmen, Aaron Rosenberg, has launched separate legal action against the company after blowing the whistle on the bribery scandal.
He has accused it of paying bribes and giving gifts to officials in 14 US states in exchange for $US100 million worth of contracts.
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