MEXICO CITY, Dec 14 (Reuters) - Environmental groups filed a lawsuit in a U.S. federal court on Wednesday, pressuring the U.S. government to sanction Mexico for failing to protect the critically endangered vaquita, the world's smallest porpoise, according to court documents.The lawsuit seeks to pressure the U.S. government to sanction Mexico under a fisheries law called the "Pelly Amendment" to the Fishermen's Protective Act, which authorizes the U.S. President to embargo imports of wildlife products, including fish, from another country.The vaquita porpoise, found in Mexico's upper Gulf of California, has over the last five years seen its population devastated to the point that it is now considered in "serious danger of extinction.""The government of Mexico is still sitting idly by as the vaquita dies," said Sarah Uhlemann, international program director at the Center for Biological Diversity (CBD), one of three NGOs which filed the lawsuit.Mexican biodiversity also faces growing risks from wildlife trafficking, much of which takes place on social media platforms, according to a recent CBD report."