The only major bank that President Donald Trump has been able to count on for financial backing was among those that were issued subpoenas Monday by House Democrats.
"It is no secret that the Democrat [sic] Party has chose to use its new House majority to launch a flood of investigations into the president's personal affairs in hopes of using anything they can find to damage him politically", said the attorneys in a letter, telling Mazars they were putting it "on notice".
Schiff said Deutsche bank had been cooperative.
A spokesperson for Deutsche Bank told the Times the bank was "engaged in a productive dialogue" with the committees.
"We remain committed to providing appropriate information to all authorised investigations in a manner consistent with our legal obligations", she said in an emailed statement.
While a few of the CEOs acknowledged internal reviews, they revealed little about client activity.
Maxine Waters, who heads the financial services committee, said the investigation was exploring "the use of the USA financial system for illicit purposes", including the potential involvement "of the president and his associates". "The Financial Services Committee is exploring these matters, including as they may involve the president and his associates, as thoroughly as possible", the committee's chair, Maxine Waters, said in a statement.
The subpoenas are part of a broader effort by Democrats to establish new information about Trump's financial dealings.
Lawmakers have focused special attention on Deutsche Bank since Trump's former lawyer and fixer Michael Cohen said Trump provided it with financial records that inflated his assets to secure loans from the company to finance real estate projects and, in one case, to attempt to buy the NFL's Buffalo Bills. On the back of a four-page summary written by his handpicked attorney general, William Barr, Trump has claimed that he has been "exonerated" of any claims of collusion or other wrongdoing.
"That's a different form of collusion, but it is equally compromising to the country because it means the president of the United States is looking out for his bank account and not for the United States of America", Schiff said in an interview on NBC in February.
In past comments Schiff has indicated that the goal of the inquiries was to see whether "any foreign actor has sought to compromise or holds leverage, financial or otherwise, over Donald Trump, his family, his business, or his associates". But it was only after Democrats won control of the House in 2018 that they gained subpoena power.
Trump's businesses have benefited from Russian investment over the years.
Deutsche Bank has provided some $2 billion in credit to Trump since 1998, The New York Times previously calculated.
House Republicans have said that Schiff and other Democrats are hounding the president with their flurry of investigations and subpoena threats.