Nippon Steel Corp, Japan’s largest steelmaker, has filed a lawsuit against Toyota and its supplier, China’s Baoshan Iron & Steel Co. Ltd., for alleged patent infringement. The automaker called the suit “regrettable.”

The steelmaker is seeking 20 billion yen ($176 million) in damages from the companies, alleging they have infringed on its patent for non-oriented magnetic steel sheets that are used in electric vehicles, reports Reuters.

The steel sheets are a critical part of electric motors that have a big impact on efficiency because of their magnetic properties that help limit energy loss.

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The suit is unusual because it is rare for a steel supplier to sue an automaker and Toyota is one of Nippon Steel’s key customers. Regardless, it has petitioned for an injunction preventing Toyota from manufacturing and selling vehicles that use the steel that allegedly violates its patents.

The company says it has taken legal action after it was unable to reach a resolution through discussions with the companies, something Toyota seems to confirm in a statement it released on the matter. It claims that it did its due diligence to ensure that the steel did not infringe on any patents.

“Concerning the electromagnetic steel sheets manufactured by Baoshan Iron & Steel Co., Ltd. (Baosteel), as well, we confirmed that there was no infringement of another company’s patent before concluding a contract,” Toyota wrote. “Because Nippon Steel mentioned to us its concerns, we confirmed again with Baosteel, which, in turn, expressed its view to us that there was no patent infringement.”