FINMA, the Swiss regulator, said the decision would bolster the bank's capital. Engineered in the wake of the global financial crisis, AT1 bonds are a form of junior debt that counts towards banks' regulatory capital. "It's stunning and hard to understand how they can reverse the hierarchy between AT1 holders and shareholders," said Jerome Legras, head of research at Axiom Alternative Investments, an investor in Credit Suisse's AT1 debt. Credit Suisse's AT1 debt had rallied earlier on Sunday amid reports that shareholders would receive something in a deal with UBS, raising hopes that bondholders would be protected. The move by the Swiss regulator could make it harder for other lenders to raise new AT1 debt, investors said.

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