Bank of America said it would no longer send trades to Credit Suisse's "ATS Crossfinder". That trading platform anonymously matches buy and sell orders for the same kinds of securities, according to the Credit Suisse website. The U.S. Securities and Exchange Commission website calls the ATS Crossfinder a "dark pool."

Bank of America sent the email to traders and hedge fund clients on Monday morning.

On Sunday, the 167-year old Swiss lender was subsumed into its larger rival UBS, which agreed to pay 3 billion Swiss francs ($3.23 billion) for Credit Suisse in a package engineered by Swiss regulators.

Credit Suisse declined to comment on the email and Bank of America also declined to comment.

The Credit Suisse rescue was backed by a massive Swiss government guarantee, helping prevent what would have been one of the largest banking collapses since the fall of Lehman Brothers in 2008.

Switzerland has pledged 260 billion francs in liquidity lines and guarantees to UBS to help smooth the takeover as Credit Suisse clients and counterparties reassess their relationship with the stricken lender.

The deal will also make UBS Switzerland's only global bank and the Swiss economy more dependent on a single lender.

(Reporting by Nell Mackenzie and Lananh Nguyen; Editing by Dhara Ranasinghe; Editing by David Gregorio)

By Nell Mackenzie and Lananh Nguyen