John Mann MP, a member of the Treasury select committee, said that RBS had been "reckless yet again" when it paid out a total of £200m worth of sponsorship fees to sports stars including the Queen's granddaughter and equestrian star Phillips, golfer Nicklaus, tennis star Murray and former motor racing champion Sir Jackie Stewart.
Mann has called for the sports stars to volunteer to opt out of their lucrative contracts. He said: "I think it would go down very well with the British public if some of them were to cancel their contracts. Some of them would become real heroes if they did."
Sir Fred Goodwin, the bank's former chief executive, agreed contracts of up to five years just weeks before he left the bank last October.
Stewart, who is said to have been paid £4m to promote RBS, said: "I am very much still with RBS. My contract has nearly two years to run and they always honour contracts."
Phillips is understood to have signed a three-year deal in 2007, but her spokeswoman said the bank had made no move to renegotiate the contract.
RBS has also spent millions sponsoring high-profile sporting events including the US and British Opens in golf, the Six Nations rugby tournament, Formula One and the NatWest series in cricket.
The bank, which is heading for a £28bn annual loss and announced that it was axing 2,300 jobs in the UK last week, said that it was obliged to honour the deals.
It is the second controvery to engulf the troubled bank in less than a week, after it was lambasted for plans to pay out an estimated £1bn in bonuses to staff. A petition against the bank paying bonuses, organised by former deputy prime minister John Prescott, collected more than 20,000 signatures.