In the 1951 case Pennsylvania Water & Power Co. et al. v. Federal Power Commission et al., the Supreme Court ruled in favor of the Federal Power Commission (FPC). The dispute arose when Pennsylvania Water and Power Company, along with other power companies, challenged FPC's authority to regulate their operations under Section 4(e) of the Federal Water Power Act. They argued that since they were not directly engaged in interstate commerce but only sold electricity wholesale to companies involved in such commerce, FPC had no jurisdiction over them. However, the court held that even though these power companies did not engage directly in interstate commerce themselves, their activities significantly affected it due to their role as major energy suppliers for businesses operating across state lines. Therefore, they fell within FPC's regulatory purview under its mandate from Congress to oversee all matters affecting interstate electric power transmission.

In the dissenting opinion for Pennsylvania Water & Power Co. et al. v. Federal Power Commission et al., it was argued that the majority's decision to uphold the Federal Power Commission's (FPC) authority over water power projects on non-navigable tributaries of navigable waters expanded federal jurisdiction beyond its constitutional limits under the Commerce Clause. The dissenters contended that such an interpretation would give Congress virtually unlimited control over all bodies of water, regardless of their connection to interstate commerce or navigation, which they believed contradicted previous Supreme Court rulings and exceeded congressional intent when passing relevant legislation like the Federal Water Power Act. They also expressed concerns about potential infringement upon states' rights and private property rights due to this broadened federal oversight.