The European Commission carried out unannounced inspections at the premises of companies active in ethylene purchasing on May 16, the EC said in a statement.
"The Commission has concerns that the companies concerned may have violated EU antitrust rules that prohibit cartels and restrictive business practices," it said.
Celanese said Thursday it found out in May that the EC had opened a competition law investigation involving certain of its subsidiaries with respect to certain raw material purchases.
Celanese has been cooperating with the EU authorities, it said.
Swiss specialty chemicals company Clariant said it was part of an ongoing competition law investigation by the European Commission, and it was assisting the relevant authorities.
