Barclays boss Jes Staley is being investigated by the financial watchdog over the bank's whistleblowing programme and will have his pay docked.
The Financial Conduct Authority (FCA) and the Prudential Regulation Authority (PRA) have both commenced investigations.
The probes concern an attempt last year by Mr Staley to identify the author of a letter that raised concerns about the bank's whistleblowing procedures.
Barclays said that Mr Staley "honestly, but mistakenly, believed that it was permissible to identify the author" of the letter.
Barclays has decided to issue the chief executive with a formal written reprimand and ensure that a "very significant compensation adjustment" be made to Mr Staley's pay packet.
The amount docked from Mr Staley's salary will be decided after the FCA and PRA investigations are over.
The investigations concern anonymous letters sent in 2016 to the Barclay's board and a senior executive raising concerns about a newly-recruited senior employee and Mr Staley's role in the recruitment.
Having been given a copy of the first letter and made aware of a second, Mr Staley initially requested that Barclays Group Information Security team attempt to identify the authors of the letters - an attempt that was ultimately unsuccessful.
Mr Staley considered the letters an unfair personal attack on the senior employee, the bank said.
Barclays, which is commissioning an independent review of its whistleblowing procedures, said both it and Mr Staley will co-operate fully with the investigations.
Mr Staley said: "I have apologised to the Barclays board and accepted its conclusion that my personal actions in this matter were errors on my part."
He continued: "Our whistleblowing process is one of the most important means by which we protect our culture and values at Barclays and I certainly want to ensure that all colleagues, and others who may utilise it, understand the criticality which I attach to it."
Barclay's board concluded that Mr Staley "made an error" in becoming involved and not applying appropriate governance around the matter.
Barclays chairman John McFarlane said he was "personally very disappointed and apologetic that this situation has occurred".
"The board takes Barclays' culture and the integrity of its controls extremely seriously," he said.
"We have investigated this matter fully using an external law firm and we will be commissioning an independent review of Barclays' processes and controls to determine what improvements may be required."
He added that Mr Staley has an otherwise exemplary record and continues to have the board's unanimous confidence and support.