Dow Europe filed a €1.1 billion ($1.26 billion) damages claim against Swiss specialty chemicals manufacturer Clariant and three unnamed firms.
The lawsuit, submitted to a German court, alleges competition law violations within the ethylene purchasing market.
This legal action follows a 2020 European Commission ruling that fined Clariant, Orbia, and Celanese for colluding to suppress ethylene purchase prices.
Clariant rejected the allegations and vowed to defend its position in court.
The Swiss company claims to possess economic evidence showing its past conduct had no impact on the market.