Prosecutors raided the offices of the country's seven major steelmakers as part of their investigation into allegations of bid rigging.

The Seoul Central District Prosecutors' Office on Wednesday dispatched investigators to the headquarters and offices of Hyundai Steel, Dongkuk Steel Mill, Daehan Steel, KISCO, YK Steel, Hwan Young Steel and Hankook Steel & Mill to secure evidence.

The companies face charges of conspiring to fix their supplies and prices before bidding on tenders by the state procurement agency between 2012 and 2018. The alleged collusion helped them post a combined order value of some five-point-five trillion won.

They are also accused of violating the fair trade law by not cooperating in an investigation by the state antitrust regulator.

In August, the Fair Trade Commission(FTC) issued a correction order and slapped combined penalties of 257 billion won. The regulator filed complaints with the prosecution against the seven firms and nine of their former and incumbent employees for not paying up.