French President Francois Hollande has already written to US President Barack Obama in defence of BNP Paribas bank, threatened with huge sanctions on charges of embargo breaches, Hollande's office said on Wednesday.
In a statement before Hollande and Obama meet for dinner, the Elysee Palace said that two months ago the French president urged Obama to take account of what it described as "disproportionate" penalities being lined up to hit the bank.
These penalties, which could also include action crimping the bank's ability to provide services in dollars, are reported to amount to more than $10 billion (7.4 billion euros) on charges that BNP broke US sanctions against Iran, Sudan and Cuba between 2002 and 2009.
The threat of such big penalties on the bank, one of the biggest in Europe, is a hot issue for French authorities, which warn that it could destabilise the financial system, cut lending to businesses and so impede economic recovery.
A diplomatic source said that the threat hanging over the bank would would be one of the issues Hollande will raise when he meets Obama for the dinner, against the background of D-Day World War II celebrations.
In the letter on April 7, Hollande "drew the attention of President Obama to the disproportionate nature of the sanctions being envisaged and of the related risks," his office said.
He said that "in respecting the independence of the justice system, the procedure should proceed on a reasonable basis directly in line with the financial regulation authorities."
The statement from the Elysee Palace is the second shot in two days from the top of the French administration.
On Tuesday, Foreign Minister Laurent Fabius said that France would support the bank in the matter, and linked it to negotiations between the European Union and the United States on a trans-Atlantic trade pact.
And the New York Times newspaper reported that the governor of the Bank of France, Christian Noyer, had visited top US officials on the case in New York last week to warn that such a fine could have much wider repercussions.
Noyer had already said in France that BNP Paribas had done nothing wrong under French, EU and United Nations rules.
Fabius said in a television interview: "If there was a fault, then it is normal that there be a sanction, but the sanction has to be proportionate and reasonable. These figures are not reasonable," he said.
The dispute "raises a very, very big problem", he added.