The Royal Bank of Scotland has warned its employees that they must have a current account with the company or face disciplinary procedures.
In a letter to staff whose salaries are paid into accounts held by other banks, RBS chief executive of retail markets Gordon Pell gives them a deadline to change their account provider.
Trade union Amicus, which originally obtained the letter after receiving thousands of complaints from aggrieved employees, has accused RBS of being "heavy-handed" in its approach.
Many banks in Britain tell their employees to take out accounts with the company, a line that RBS has taken in its defence this morning.
But Amicus spokesperson Alison Maclean told the Today programme that this view was "not something that the union would view as essential".
"We believe that the employer's approach in this has been heavy-handed and certainly not conducive to good employee relations," she explained.
"Where the problem has arisen is with employees [who] have chosen to have their salary paid into another bank account.
"And there're also employees that have joined the group from other constituent organisations such as Direct Line or Churchill Insurance.
"It wasn't a problem a year ago, two years ago, and now all of a sudden it is a problem," Ms Maclean went on to say.
"And what we're talking about here is employees who have been loyal to the bank, dedicated, have never had any kind of issue in terms of proposed disciplinary action and they now find themselves in a situation where potentially they could face disciplinary action for failure to have their salary paid into a group bank account."
RBS, which also owns NatWest along with Direct Line and Churchill Insurance, has insisted that all employees were already aware of this aspect of company policy.
A spokesperson for the bank said: "In common with industry practice, our terms and conditions require staff to open a current account with us for the payment of their salary.
"This is made clear to all staff during the interview process and forms part of the overall reward package we offer which includes a wide range of very generous benefits including financial deals.
"Our staff are at complete liberty to run accounts with other providers if they wish," the representative added.