The Conservative Party treasurer has faced calls to quit after he agreed to host a House of Lords dinner as part of a £6,000 entertainment package for American Express cardholders.
Lord Fink, a major Tory donor and David Cameron's chief fundraiser, was accused of breaching parliamentary rules by sponsoring the private dinner.
It was part of a 9,391 dollar-a-head "Wimbledon Championships" package available to AmEx Platinum and Centurion card-holders, according to the Bureau of Investigative Journalism and The Independent.
It was advertised as a "one-of-a kind opportunity to advance your lifestyle" and also included two days of tennis, accommodation at the Dorchester hotel in Park Lane and a drinks reception with former tennis pro John McEnroe.
Lord Fink was appointed Tory treasurer in March to replace Peter Cruddas, who resigned after being caught promising access to the Prime Minister in return for large donations to the Conservative Party.
The Tories said Lord Fink was no longer sponsoring the dinner after it was brought to his attention that it may be in breach of the rules. A source said: "If there was a mistake then it was a completely innocent one."
Jon Trickett, shadow minister for the Cabinet Office, urged hedge fund millionaire Lord Fink to consider his own position.
"This is a flagrant attempt to breach the rules of Parliament. It leaves a very nasty taste to suggest that you can buy access to the House of Lords, and it cheapens democracy," Mr Trickett said.
"Lord Fink, who is a major donor to the Tories, should consider his position as Treasurer of the Conservative party and if he refuses to do so the Prime Minister should sack him.
"To have one Tory treasurer in trouble for appearing to sell access to Number 10 is bad enough, some might think that now to have a second Treasurer apparently in breach of the code of conduct is a sign of systemic moral failure in the high command of the Conservative Party."
Lord Fink said he had agreed to sponsor the dinner in return for a donation to Guy's and St Thomas' Hospital in London.
"This event has been held in the Lords on several occasions in the past and I agreed to sponsor it this year in return for a sizeable donation to a major hospital," he said.
"I have no commercial interest in Amex and there was never any question of me profiting from sponsoring it."
A Conservative Party spokesman said: "Lord Fink cancelled his sponsorship of the event at the beginning of last week as soon as he received advice that there might be an issue with it."