Royal Bank of Scotland has sparked a fierce row with unions by threatening 14,000 staff with disciplinary action unless they open and have their salary paid into a current account with the group.

An RBS spokeswoman refused to rule out the possibility that employees could ultimately face the sack.

The bank, home to Direct Line, Churchill and NatWest, has written to thousands of employees warning them they will be in breach of group policy unless they act.

In a letter seen by TimesOnline, Gordon Pell, chief executive of retail markets, tells staff he has “noticed” they are still having their salary paid into an account from outside the RBS Group.

He warns that if they fail to meet a deadline for switching from a rival: “I will be obliged to write directly to your line manager asking them to progress this matter according to the group’s disciplinary policy.”

Union leaders at Amicus claimed their helpline has been “jammed” with calls from angry staff furious over RBS’s tactics.

Rob MacGregor, national officer, said: “If you work for Tesco you won’t be disciplined for buying your groceries from Sainsbury's. RBS’s disproportionate and heavy-handed approach is counter-productive and bad for morale. We are calling on the bank to reconsider its position.”

The move is the latest in line of high-profile gaffes by Britain's banks. An investigation earlier this week by the BBC found that Barclays was charging customers £40 in administration fees that in fact cost the bank only £1.50.

Amicus said that up to 14,000 of RBS’s 100,000 staff are affected by the move. Mr MacGregor said RBS had refused to rule out dismissing employees who fail to open an account.

An RBS spokeswoman would only say that the bank would be “very disappointed”. She insisted the approach was in line with common industry practice and said staff were at “complete liberty” to run other accounts with other banks.

Barclays and Lloyds TSB have similar policies but one industry insider said she had never heard of such a tactic to make employees comply. She said: “This seems a bit over the top.”

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