(Adds details on market volatility, ethics memo) WASHINGTON, Feb 2 (Reuters) - U.S. Treasury Secretary Janet Yellen is calling a meeting of top financial regulators this week to discuss market volatility driven by retail trading in GameStop Corp and other stocks. Yellen will convene the heads of the Securities and Exchange Commission, the Federal Reserve, the Federal Reserve Bank of New York and the Commodity Futures Trading Commission, a Treasury official said on Tuesday. Yellen sought and received permission from ethics lawyers before calling the meeting, according to a document seen by Reuters, and to engage on wide-ranging issues in the financial services industry. Yellen"s decision to seek the waiver followed a report here by Reuters that because of speaking fees she was paid by a key player in the GameStop saga, hedge fund Citadel LLC, she may need to seek an ethics waiver in order to deal with matters involving the firm. The Treasury official, who declined to be identified by name, said the meeting would be held this week, possibly as early as Thursday. “Secretary Yellen believes the integrity of markets is important and has asked for a discussion of recent volatility in financial markets and whether recent activities are consistent with investor protection and fair and efficient markets,” Treasury spokeswoman Alexandra LaManna said in a statement to Reuters. Yellen’s action comes after days of gyrations in the shares of video-game retailer GameStop driven by retail investors that have made or lost billions of dollars for hedge funds and other investors in recent weeks. Retail trading activity has also driven up silver prices in recent days. GameStop shares more than halved in value on Tuesday and silver prices retreated as the Reddit-driven trading frenzy that roiled stock and commodity markets died down, at least for now. GameStop shares closed down 60% at $90. They are now worth less than a fifth of their high of $483 last week. ADVERTISEMENT The saga is likely to expedite a regulatory review of the ever-larger role played by non-bank firms in the financial markets, regulatory experts say. Treasury ethics attorneys have given Yellen flexibility to work on any related issues that come up, with no limits on current or future markets, the Treasury official said. In the memo granting Yellen permission to call the meeting of regulators, a Treasury ethics official, Brian Sonfield, said it would be “difficult, if not impossible” for Yellen to recuse herself from matters involving market volatility. “You are the Secretary of the Treasury, the duties of which require you to be involved in a broad array of matters focused on these sectors,” Sonfield wrote. “Issues relating to these sectors could arise at any time without the opportunity for consultation with the ethics office. These circumstances make it difficult, if not impossible, for you to recuse from matters relating to these sectors and also argue in favor of prior authorization.” Reporting by David Lawder and Trevor Hunnicutt; Additional reporting by Andrea Shalal; Editing by Heather Timmons, Cynthia Osterman and Peter Cooney Our Standards: The Thomson Reuters Trust Principles.