Federal Reserve Chairman Jerome Powell instructed staff to review the central bank’s ethics rules for adequate financial activity after it was revealed that several senior central bank officials had multi-million dollar stock deals in 2020 while others were holding significant investments.

The news of Powell’s investigation came after Senator Elizabeth Warren sent 12 letters to the presidents of the Fed’s regional banks calling for stricter ethics from the country’s top central bank officials.

The Massachusetts Democrat urged every Fed president to ban high-ranking officials in any regional office from owning and trading individual stocks.

Last week, the financial disclosures filed by the Fed’s 12 regional presidents showed that some had actively traded in 2020 while others held million dollar financial positions without making changes to their portfolios.

A Fed spokesman told CNBC that Powell ordered a “new and comprehensive look at the ethical rules on eligible financial holdings and activities of senior Fed officials” last week.

Powell ordered the review “because the confidence of the American people is essential for the Federal Reserve to carry out our important mission effectively,” the spokesman said. “This review will help find ways to further tighten these rules and standards. The Board of Directors will make changes as necessary and any changes will be added to the reserve bank’s code of conduct.”

Documents released last week showed that Dallas Fed President Robert Kaplan did multiple deals worth $ 1 million or more in individual stocks like Apple, Amazon and Delta Air Lines over the past year.

Boston Fed President Eric Rosengren had interests in four real estate investment trusts and several purchases and sales of similar real estate vehicles, the files said. He also held shares in Pfizer, Chevron, and AT&T. His investments ranged from tens to hundreds of thousands of dollars.

Other Fed presidents, such as Richmond Fed President Thomas Barkin, reported little to no trading activity, but announced several financial holdings in excess of $ 1 million.

His stakes included Coca-Cola shares worth more than $ 500,000 but less than $ 1 million. Barkin’s largest holdings, valued at least $ 1 million, included a variety of exchange-traded funds and mutual funds overseen by outside managers.

For example, he had a stake of at least $ 1 million in Vanguard’s Energy Fund Admiral Shares, an investment fund that invests in energy companies such as ConocoPhillips, Marathon Petroleum and BP.

Even the appearance of self-governance at the Fed could prove problematic for an institution charged with impartial oversight of US employment and inflation.

The business was quickly scrutinized given the crucial role the Fed played in steering the US economy and its impact on interest rates and liquidity markets.

The Covid-19 pandemic and the subsequent recession increased the power of the Fed in 2020. Congress allows the Fed, with the approval of the Treasury Department, to take a wide range of emergency lending measures to flush the economy with cash during times of crisis.

Rosengren, Barkin and Kaplan serve as presidents of three of the Fed’s 12 regional banks, which span the country. The presidents of the regional banks take turns on the Federal Open Market Committee, the Fed’s political body that sets interest rates for the entire economy.

Amid public backlash, both Kaplan and Rosengren have agreed to sell their individual holdings of shares.

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Separately, Warren sent letters to all the governors of the Fed’s regional banks calling for stricter restrictions on the types of financial activities officials can participate in.

Each letter, all dated September 15, was similar to the next except for the two addressed to Kaplan and Rosengren.

“When the Fed took exceptional measures to manage the risks to the economy and the banking and financial system posed by the COVID-19 pandemic, you and your colleague Eric Rosengren did extensive trades in individual stocks and real estate funds,” Warren wrote in her letter to Kaplan.

This trade, she added, “has raised concerns about conflicts of interest among senior officials with far-reaching political influence and exceptional access to information about the economy”.

The Fed played a leading role in helping the US economy recover from the worst of the coronavirus recession.

Economists say his political independence enabled him to act faster than Congress, and that his $ 120 billion monthly purchase of U.S. debt and mortgage-backed securities helped support countless companies operating in the passed out last year.