The American Bar Association's annual conference is facing a crisis after grossly over-estimating registration numbers for its London conference this summer.
Its $1m (£664,691) emergency fund could be used for the first time in a bid to stop costs spiralling out of control.
Only 3,000 lawyers have signed up for the event in July instead of the projected 8,000.
The low registration leaves the ABA facing a potential financial crisis and the ABA Board of Governors has empowered its executive committee to reduce costs.
But it has already altered one venue by dropping Westminster Hall in favour of the cheaper Queen's Royal Gallery in a bid to cut costs. The biggest event, the ABA President's reception at the Tower of London, will have to be scaled back.
A UK spokesman says: "The committee is meeting to make sure that there is no downgrading of the event."
It is understood the ABA needs at least 5,000 delegates to break even on the event. The last ABA London conference, held in 1985, attracted more than 9,000 people.