The US Securities and Exchange Commission's Office of Inspector General (OIG) spent months investigating who leaked information related to the JPMorgan 'London Whale' incident to Reuters.
Reuters is also the only agency to have also reported on the OIG probe. This was conducted after the media group reported on the closed-door meeting between the watchdog and JPM on 12 September 2013, regarding a settlement over the massive London Whale trading loss.
The story revealed that the regulator approved its portion of a $700m (£415m, €523m) civil settlement with JPM in a split vote. It also reported other details, including that two of the five commissioners had recused themselves from the decision.
Reuters then published another story afterwards detailing more non-public information.
"It's the job of journalists to report vigorously on the workings of government, and to provide readers with news that some may prefer to keep secret," said Reuters editor-in-chief Stephen Adler.
"It is in that spirit that Reuters covers the SEC and other agencies of the US government, and we plan to continue to do so while protecting the confidentiality of our sources."
Reuters also claims "the investigation is the latest example of the Obama administration's aggressive moves to try to plug leaks of non-public information to the media."
The SEC has not responded to Reuters for comment.
What Was the London Whale Incident?
In May 2012, trader Bruno Iksil, nicknamed the 'London Whale' for his preference for huge trades, and his colleagues at the London unit of JPM's Chief Investment Office (CIO) lost billions of dollars through bad bets in a portfolio that was specifically designed to hedge the bank's risk exposure.
This prompted an investigation by several US authorities and JPM chief, Jamie Dimon, was forced to explain to the US Senate the regulatory protocols of the CIO's risk managers.
Initially, Dimon dismissed the losses as a "tempest in a teapot," but later said it was "the stupidest and most embarrassing situation I have ever been a part of."
The bank has since stumped up nearly $1bn in fines related to the London Whale trading scandal.
The US has also indicted a number of individuals.