Fallout from a two-year Department of Justice investigation into cheating in the $16 trillion market for U.S. government debt reportedly could be the biggest political and financial test for the Trump administration.

Federal prosecutors have recently subpoenaed several banks as part of a criminal investigation into possible manipulation of the U.S. Treasuries market, people familiar with the matter told Bloomberg.

UBS Group AG, BNP Paribas SA and the Royal Bank of Scotland Group Plc received subpoenas last month seeking information on the $14 trillion market, the people said. New York-based Morgan Stanley has also received a subpoena, one person told Bloomberg.

A series of class action lawsuits have accused various banks and brokerages of conspiring to manipulate U.S. Treasury auctions, Reuters reported.

The lawsuits have alleged that the banks colluded to manipulate Treasury Department auctions and the pricing of Treasury securities, as well as derivative products such as futures, whose