US President Donald Trump, along with his family and businesses, on Monday sued Deutsche Bank and Capital One in an attempt to stop them from complying with Congressional subpoenas issued as part of a probe into foreign political influence.

The subpoenas -- which the Trumps described in their suit as “intrusive and overbroad” -- were issued to several banks by the Democratic-majority House’s intelligence and financial services committees, which are looking into the president’s finances as part of a larger probe into election meddling by Russia.

The lawsuit is the latest step in Trump’s fightback against the Democrats, and alleges that the subpoenas have “no legitimate or lawful purpose.”

“The subpoenas were issued to harass President Donald J. Trump, to rummage through every aspect of his personal finances, his businesses, and the private information of the President and his family, and to ferret about for any material that might be used to cause him political damage,” said the suit, filed with the US federal court in the Southern District of New York.

“No grounds exist to establish any purpose other than a political one.”

The suit accuses Congress of stepping beyond its law-making mandate into law enforcement, and says the subpoenas violate the financial privacy rights of Trump and his family.

Deutsche Bank was one of the few major Western financial institutions to continue to lend to Trump’s real estate empire after several of its casinos went bankrupt in the 1990s, resulting in claims by creditors valued at $330 million in present-day dollars.

The Trumps want to block any such disclosures, and have requested in their latest lawsuit “a permanent injunction prohibiting Deutsche Bank and Capital One from disclosing, revealing, delivering, or producing the requested information, or otherwise complying with the subpoenas.”

Their filing also argues that Congress is seeking information about “events that occurred while President Trump was a private citizen, years before he was even a candidate for public office.”