WASHINGTON (Reuters) -The U.S. Supreme Court declined on Monday to hear a challenge by broker-dealer Alpine Securities claiming that the enforcement power given by the federal government to the Financial Industry Regulatory Authority, Wall Street's self-regulator, is unconstitutional. The justices turned away Salt Lake City-based Alpine's appeal of a lower court's ruling that allowed FINRA to move forward with an enforcement action against the company for allegedly stealing more than $54.5 million from customers. FINRA, a non-governmental self-regulatory organization, is responsible under federal law for supervising broker-dealers in the United States with the aim of protecting investors and the integrity of securities markets.