The banks said they had acted within regulatory requirements but declined to offer fuller explanations.
Le Pen is smarting from defeat in this year's presidential and parliamentary elections, during which she accused French banks of being politically biased for not lending to her campaigns.
"This is an attempt to suffocate an opposition party, and no democrat should accept that," Le Pen told a news conference, calling on President Emmanuel Macron and other political parties to back her National Front (FN).
Le Pen said the FN would file a complaint against Societe Generale and its subsidiary, Credit du Nord. She also plans a complaint against HSBC for closing a personal account of hers.