Just recently (October 2021), Nippon Steel surprised many by suing not only a Chinese steel company Baoshan Iron & Steel but also its customer, Toyota, for infringing its own patent rights on steel products (*1). Now, Nippon Steel has surprised us even more by suing Mitsui & Co (*2). This is because Mitsui & Co does not manufacture any related products.
In fact, the Patent Law defines infringement not only as the act of “producing” an infringing product, but also as the act of “selling” or “using” it. So, the patent owner can enforce the patent right (requesting for an injunction and/or seeking damages) against the manufacturer, the wholesaler, the retailer of the infringing product, or against all of them. This means that any company in the supply chain can be involved in a patent dispute.
Therefore, when dealing with products of other companies, you should also pay attention to whether or not the products infringe on third parties’ intellectual property rights.