The regulatory division of the National Association of Securities Dealers has combined with New York Stock Exchange Regulation Inc., the regulatory division of the New York Stock Exchange.

The U.S. Securities and Exchange Commission, which will oversee the new organization, approved the merger Thursday, allowing the 2 groups to merge their oversight functions.

Known as FINRA, the organization will be the largest nongovernmental regulator for securities brokers and dealers doing business with the public in the United States. FINRA will be responsible for rule writing, firm examination, enforcement, and arbitration and mediation functions, in addition to functions previously supervised by NASD, including market regulation for NASDAQ, the American Stock Exchange, the International Securities Exchange, and the Chicago Climate Exchange.

FINRA will oversee more than 5,000 securities firms and 666,000 registered representatives.