A New York banking regulator suspended the French bank from clearing transactions in energy trade finance for the whole of 2015 as part of a punishment for violating U.S. sanctions against Sudan, Cuba and Iran. The suspension also included financial penalties of nearly $9 billion.

"Without getting help with the clearing, BNP will simply not be able to operate its energy trade finance division," a source at a trading company which works with BNP said.

The energy trade finance business accounted for as much as 5 percent of BNP's revenues in 2006 but was scaled back after the 2008 financial crisis and then again after the U.S. probe. It now only represents 1 percent of overall revenues although still accounts for hundreds of jobs.

U.S. dollar typically transactions pass through one of two major clearing systems in New York where large volumes of the main currency for global trades are readily available.

Despite the suspension imposed by the New York regulator, the terms of the punishment left the door open for the French bank to pay others to do the job.

The suspension of dollar clearing was on business lines that were the central points of wrongdoing, according to the New York Department of Financial Services.