Abu Dhabi Commercial Bank is suing Credit Suisse and credit rating agency Standard & Poor's, alleging it was misled over a 2007 investment that went sour.
The government-controlled Emirati bank said Thursday it filed the lawsuit against the companies and others in New York.
ADCB alleges that Credit Suisse failed to disclose conflicts of interest and provided misleading information about the investment, known as Farmington.
It claims S&P made inaccurate ratings tied to the investment.
ADCB CEO Ala'a Eraiqat says the lawsuit aims to protect the bank from potential losses, but he doesn't expect it to have a major effect on the company's earnings.
Credit Suisse and S&P did not immediately comment on the lawsuit.