BlueScope could have to pay out more than $100 million in fines if it loses its price-fixing court case.
The Australian Competition and Consumer Commission has launched proceedings in the federal court over allegations former employee Jason Ellis engaged in cartel conduct.
The ACCC statement of claim lists 12 instances where, between September 2013 and June 2014, Ellis allegedly tried to induce rival steelmakers to set a fixed price for steel.
BlueScope has said planned to "strongly defend the proceedings".
The steelmaker had conducted an "internal investigation" into the ACCC allegations and believed no current or former employees mentioned by the ACCC in the court documents engaged in cartel conduct.
According to the ACCC's statement of claim, each of the 12 breaches of the Competition and Consumer Act carries a choice of penalties - both of which are severe.
At the top end, each proven breach can cost $10 million, or 10 per cent of the annual turnover of BlueScope during the 12 months prior to the last alleged offence in June 2014 - whichever is greater.
READ MORE: CEO 'was aware' of price-fixing plan - court
In the 2013-14 financial year BlueScope recorded $249 million in earnings - 10 per cent of that is $24 million.
So the maximum penalty could be $288 million - around a quarter of the steelmaker's earnings in the last financial year.
The ACCC also alleges Ellis threatened overseas manufacturers with anti-dumping claims unless they increased the price of the steel they sold in Australia.
News of the ACCC's cartel conduct investigation came in August 2017, when former BlueScope CEO Paul O'Malley mentioned it at the end of the company's financial year announcement.
He said the investigation "involved a small number of BlueScope employees".
While nine BlueScope employees are named in the court documents - including new CEO Mark Vassella, only Ellis is named as a party to the court case.