The Government has been urged to withhold any more payments to banks which advised the Government on its controversial privatisation of the Royal Mail amid continuing complaints that the taxpayer has lost hundreds of millions of pounds over the sell off.
The sale will come under the spotlight again tomorrow when MPs question bankers who provided valuations of the company before the flotation.
The Communication Workers Union (CWU) said any further payments should be withheld on the basis that banks undervalued the company.
General secretary Billy Hayes said: "Hundreds of millions of pounds of taxpayers' money have been lost because of the failure of the Government and its advisers to accurately value the company. In other situations this would be gross incompetence or even theft. Private shareholders have lined their pockets at the expense of the taxpayer following the huge leap in the share price.
"At the very least the institutions which advised the Government should not receive any further payments - which are discretionary. Serious consideration should be given to claiming back fees paid for shoddy advice which has left the client - the taxpayer - out of pocket.
Bosses from six banks will appear before the Business Select Committee in Parliament tomorrow as controversy over the sale continues.
Those due to appear are John Mayne, Managing Director, UK Client Coverage, JP Morgan; Ben Storey, Head of UK Investment Banking & Broking, Citibank; Gert Zonneveld, managing director, Co-Head of Research, Panmure Gordon; James Agnew, chairman of UK Corporate Broking, Deutsche Bank; James Robertson, managing director, UBS and Richard Cormack, managing director, Co-Head of Equity Capital Markets, Goldman Sachs.
Business Secretary Vince Cable and Business Minister Michael Fallon will appear before the committee next week, as well as a representative from Lazard, the institution that vetted the flotation price.
The committee said it wanted to follow up on issues that have arisen following the share flotation.
Goldman Sachs and UBS were the investment banks that ran Royal Mail's flotation last month, while JP Morgan, Citibank and Deutsche Bank missed out on running the share sale, while broker Panmure
Gordon attacked what it said was the undervaluation of Royal Mail.
The share price was set at 330p, valuing Royal Mail at £3.3 billion, but the shares jumped by over a third on the first day of trading, and broke through the 500p mark within a week.
The share price today stands at more than 550p. The CWU said this means the Government
undervalued the company by more than £2 billion.