The executives were asked to ensure staff are aware of the regulations and they have the necessary procedures in place to protect any whistleblowers, according to the sources, who asked not to be named because of the sensitivity of the matter.
The Financial Conduct Authority declined to comment as did Royal Bank of Scotland (>> Royal Bank of Scotland Group plc), Barclays (>> Barclays PLC), Lloyds Banking Group (>> Lloyds Banking Group PLC), and HSBC (>> HSBC Holdings plc).
The calls to the banks are a sign of how seriously the regulator is taking this issue and show concerns that other banks may not have enforced the policy, one of the sources said.
"They didn't want to be caught with their trousers down and to find out that no one is really enforcing the rules," said a senior executive at one of Britain's largest banks.
Earlier this week, Barclays said it had reprimanded Chief Executive Officer Jes Staley and would cut his bonus after he twice attempted to identify the author of a letter that revealed "concerns of a personal nature" about an unnamed senior employee.
The Financial Conduct Authority and the Bank of England's Prudential Regulation Authority, which vetted Staley's appointment as CEO, are investigating the bank and Staley to see what other penalties might be warranted.
The case has raised concerns about how much the culture at large banks has really changed since the 2007-2009 global financial crisis, when misconduct by bankers led to a slew of lawsuits and regulatory probes.
Since then banks have been at pains to demonstrate they have mended their ways.
Measures at Barclays, for example, have included a series of training programs reinforcing conduct policies, changing employee performance measurements to better emphasise conduct and having CEO Staley write several internal memos about the importance of the bank's reputation.
Lawmakers have likewise tightened their scrutiny, demanding banks make clearer who is accountable for executives' behaviour and strengthen protections for those who call attention to misbehaviour.
Former JPMorgan banker Staley's attempts to hunt an internal whistleblower down will become a test case for whether these claims of reform are more than lip service, lawmakers and lawyers said this week.
By Andrew MacAskill and Lawrence White