HONG KONG—A swell of opposition against shark fin soup—a traditional but increasingly controversial Chinese dish—gained backing from the luxury Shangri-La hotel chain just days before Lunar New Year, underscoring efforts world-wide to stop the hunting and trading of the endangered fish.

Shangri-La Asia Ltd. said it would ban shark fin from all of its 72 hotels, most of which are in Asia. About 95% of all shark fin is consumed within China, according to marine conservation...