Donald Trump doesn't want anyone to see his tax returns. Not the public. Not Congress.

But at least one group has peered into the carefully guarded trove and could provide some insight - a team from Deutsche Bank.

Donald Trump has faced pressure to reveal the contents of his tax returns. Credit:Bloomberg

The bankers got a look before agreeing to lend to the Trump Organisation in 2012 - access that was described by two people familiar with the interaction. It was all part of a fresh start on a banking relationship that had soured after the financial crisis, descending into litigation over a Chicago project.

After a recent subpoena, Deutsche Bank was prepared to begin on May 6 turning over details to Congress about that relationship and its loans to Trump family businesses. Now, Trump and his family have sued to stop the flow of information. That follows an earlier lawsuit against Democrats and Trump's outside accounting firm to prevent similar subpoena responses. Meanwhile, the Treasury Department has balked at supplying Trump's tax filings from the Internal Revenue Service, a standoff that could fuel protracted court battles over the extent of congressional oversight.