France ’s so-called “anti-fast fashion” law has hit a snag.

Writing in an April 15 reaction, the European Commission said that Loi Violland—a bill designed to curb overconsumption by regulating the environmental impacts of low-cost, high-volume brands—runs afoul of the EU single market, violates existing e-commerce regulations and is otherwise “incompatible with Union law.”

The letter argued that Loi Violland’s restrictions on advertising that encourage overconsumption violate the “country of origin” principle under EU law, which requires that a digital service provider should only be subject to the regulations of the member state where it is established.…