Shark-fin soup is considered a delicacy in Chinese culture and is often eaten on special occasions.
Frank Lee, president of the Organization for Justice and Equality, said that many Chinatown restaurateurs misinterpreted the law when it took effect. Many restaurants still have shark fin on the menu.
"If a restaurant buys shark fin from an importer, the restaurant cannot resell," Lee said. "That's the problem. That means importers have nowhere to sell their shark fin."
Importers have until June 30 to dispose of their stock. Since restaurants are no longer buying, their only option is to sell directly to consumers.
Lee said the law is unfair to restaurant owners and customers who have been consuming shark-fin soup all their lives.
In January, a federal court rejected a suit by two Chinese-American groups that sought to block the ban. The groups argued that the law violated their civil rights because it targeted a food item that plays an important cultural role.
Before the ban, California had the largest market for shark fins outside Asia, the AP reported. Fins can sell for $600 a pound, and the soup can cost as much as $100 a bowl.
Critics of shark-finning, as the practice is known, cite not only humane concerns but also conservation concerns. Twenty-six species of shark are endangered, and another 115 species are considered vulnerable or near-threatened, according to Defenders of Wildlife. And as top predators in the ocean, the decline of shark populations has the potential to disrupt entire ecosystems, Christopher Chin of the San Francisco-based Center for Oceanic Awareness, Research and Education told The Washington Post in 2011.
Sports fishermen who catch a shark legally are still allowed to keep the fin for personal use or to donate it.
In addition to California, Washington, Oregon, Hawaii and Guam have also banned the shark-fin trade.