Entitled "Just hit budget!", it lists a set of principles employees should follow to grab as much cash as possible.
One section reads: "Rope: Sometimes you need to let customers hang themselves.
"You have gained their trust and they know what's coming if they fail to deliver."
The letter is sure to reignite a row over the GRG, which RBS bosses insist was not systematically trying to destroy customers.
It was only made public after demands from the Treasury Select Committee chairman Nick Morgan, a Tory MP.
Labour MP Wes Streeting, a member of the committee, said: "Most people reading this would be absolutely horrified that a well-known and previously respected brand would behave like a bunch of sharks showing no duty of care to their customers whatsoever.
"It's absolutely appalling, and no wonder the committee has had to persistently and doggedly drag this information out of them."
The note dates from 2009, after the bank had been handed £46 billion ($87.4b) of taxpayers' money to keep it afloat.
Thousands of small companies were struggling at the time as the country was mired in recession following a financial meltdown caused by RBS and its fellow banks.
Any businesses struggling to pay back debts to the lender were dumped into the GRG – theoretically with the aim of helping them get back on their feet and protecting the jobs of their workforce.
But the memo tells a very different story.
The author urged workers to lumber companies with sanctions, which ratchet up fees if firms in difficulty are unable to pay their bills.
Staff were told they must "deliver monthly fees or else", and to sign customers up for deals 'they cannot afford' so penalty costs could be imposed.
The memo said that "missed opportunities will mean missed bonuses".
It added that business owners should always be pressured into signing documents as "if they sign, they can't complain".
The author cautioned there is no such thing as a perfect deal but adds that if managers are unhappy that fees are not high enough on the one side, and on the other the level of charges means the "customer's unhappy, then you probably have the balance right".
The document outlined "16 ways to generate income" but does not mention customers' welfare once.
Details included avoiding "round number fees" as these may not sound convincing – because "£5,300 sounds as if you have thought about it, £5,000 sounds like you haven't".
It says all customers must be charged a minimum monthly fee of £500, and suggests that a customer with debts of £2million who is already struggling should be charged fees of £16,000 a month, for example, as 'they normally cannot afford this and you can leverage an upside'.
RBS's current boss Ross McEwan said the note was written by a junior manager who no longer works for the lender, and was only circulated around three GRG offices.
In a letter to Mrs Morgan, he said: "For the avoidance of doubt, the language used in the document was completely unacceptable and the bank does not condone it.
"It does not reflect bank policy or guidance, either at the time it was written or today."
The bank has launched a £400 million compensation scheme for GRG customers who can prove they were mistreated, and is refunding any complex fees charged.
A study by the City watchdog found that 92 per cent of viable businesses which ended up in the GRG were hit by "inappropriate action" at the bank.
At its peak, the unit handled 16,000 companies – meaning thousands of entrepreneurs and family owners will have been affected by these mistakes.
The Financial Conduct Authority has refused to publish a full version of its report, which is thought to give details of who in management knew what about the scandal.
