This is a provision of the Dodd-Frank financial reform act of 2010 that gives U.S. federal regulators the power to break up or otherwise constrain the activities of large financial institutions - if such firms pose a “grave risk” to the system.
Named after Democratic congressman Paul Kanjorski of Pennsylvania, chairman of the Capital Markets Subcommittee of the House Financial Services Committee, this part of the legislation represents a major change in the rights and responsibilities of regulators. There are potential parallels with the Sherman Antitrust Act of 1890 - creating the legal basis for preemptive action against overly powerful big business.
It remains to be seen if regulators will use the powers thus granted, for example against firms that are judged otherwise "too big to fail." But, as Mr. Kanjorski emphasised, “If just one regulator uses these extraordinary powers [to break up too big to fail banks] just once, it will send a powerful message,” that would “significantly reform how all financial services firms behave forever more.”
The power to decide on whether to use the Kanjorski Amendment rests with the Financial Stability Oversight Council (FSOC). 
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This would allow regulators to break up even healthy financial companies, a move that is worrying leading US institutions.
The amendment would cover "insurance companies, banks, hedge funds, whoever may be causing systemic risk", said Mr Kanjorski. "Most of us yearn for the day when the phrase 'too big to fail' is no longer a part of our vocabulary. Through responsible action advocated in this amendment, we can make that a reality."
Large financial institutions had lobbied for the amendment to be withdrawn or modified, complaining that it would harm US competitiveness.
Administration officials had rejected incorporating bank break-ups into regulatory reform, as a return to the Depression-era Glass-Steagall Act, which forced a separation of commercial and investment banking, would not prevent a repeat of the financial crisis.