WASHINGTON (Reuters) - The United States said on Friday it was appealing a World Trade Organization ruling against U.S. dolphin-safe labeling measures for tuna in a longrunning spat with Mexico closely watched by environmentalists. "Our dolphin-safe labeling measures for tuna products provide information for American consumers as they make food purchasing decisions for their families," said Andrea Mead, a spokeswoman for the U.S. Trade Representative. "Our decision to appeal the WTO ruling in this case demonstrates the commitment of the United States to our dolphin-safe labeling measures," Mead said in a statement. Under the United States' dolphin-safe labeling provisions, producers of tuna products - whether foreign or domestic - have the option of labeling tuna products that meet the standards of the U.S. provisions as dolphin safe, USTR said. One such condition, challenged by Mexico, is that the label cannot be used if dolphins are purposefully chased and encircled in order to catch tuna. Some Mexican fishing vessels use this method when fishing for tuna. The United States has argued the matter should be addressed through dispute settlement proceedings of the North American Free Trade Agreement, rather than the WTO. However, Mexico has preferred to go through the Geneva-based world trade body. If the United States loses the appeal, it could require to amend its dolphin-safe labeling laws or face possible Mexican trade sanctions. Reporting by Doug Palmer, Editing by Doina Chiacu