GOLDMAN SACHS vowed to vote in favour of the merger between the New York Stock Exchange and Archipelago, the electronic trading firm, and promised to vote against any alternative takeover while the investment bank was acting as an adviser to both sides in the $6.2 billion (£3.5 billion) deal.

The merger proposal, known as a Draft S4 and filed this week with the US Securities and Exchange Commission, spelt out the agreements struck between Goldman and the NYSE while the deal was being discussed. Goldman’s private equity business owns 15 per cent of Archipelago, while its NYSE trading firm owns or controls 113 seats of the NYSE, giving the group a massive interest in NYSE Group, the name given to the proposed combine.

In early February Goldman agreed to be a “marriage broker” between NYSE and Archipelago, suggesting that they get together to form the $6 billion company. A month later Goldman’s private equity business entered into an agreement with the NYSE that it would use its Archipelago shares to vote in favour of the deal, while agreeing not to support any other offer for the company.

The Draft S4 states that Goldman would oppose “any other action that would reasonably be expected to impede, delay, postpone . . . the transaction contemplated by the merger”.

Goldman’s controversial decision to act as marriage broker to both companies has angered some NYSE members. John Thain, the chief executive of the NYSE, used to be Goldman’s finance director and was one of the architects of Archipelago. The Draft S4 states that Mr Thain stayed out of all negotiations about the retention of Goldman as adviser to the merger partners.

Bill Higgins, chairman of the NYSE Equity Members’ Association, said: “I have thought their involvement in this was wrong right from the start. Goldman should not have been involved. No matter what they say, it looks bad.”

An NYSE source said that the agreement with Goldman was also struck with General Atlantic, another big Archipelago shareholder, while there were “Chinese walls” between the bank’s advisory and private equity arms. “This is a standard agreement and represents no conflict,” the source said.

Goldman declined to comment. Draft S4 also contained a so-called “fairness opinion” written by Lazard, the investment bank. It was hired to write the opinion to ease fears about the apparent conflict of interest facing Goldman Sachs. Lazard determined that the NYSE, as a standalone company, was worth between $3.5 billion and $4.1 billion.

Mr Higgins balked at the Lazard opinion, however, as the seat-holder had paid for his own independent valuation of NYSE that determined the exchange was worth $7 billion.

Prices of Archipelago shares and NYSE seats have risen, bringing Goldman's expected rewards from the deal to more than $100 million. The firm also gets a $3.5 million advisory fee.

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