Arcelor SA said Thursday it is accusing rival Mittal Steel Co. in a lawsuit of illegally copying a type of steel that it makes for the auto industry. Mittal, which has made an unsolicited $27 billion bid for Arcelor, called the suit “without merit.”

Arcelor spokesman Jean Lasar said the suit was not connected to Arcelor’s efforts to fend off Mittal’s takeover bid, which the company has rebuffed.