The US Supreme Court has sided with Wall Street underwriters and has ruled that an antitrust lawsuit against them involving the pricing of initial public stock offerings (IPOs) cannot go forward.

By seven votes to one, the judges yesterday reversed a ruling by a US appeals court that the lawsuit by buyers of internet and technology stock issues in the late 1990s could proceed.

"We must interpret the securities laws as implicitly precluding the application of the antitrust laws to the conduct alleged in this case," Mr Justice Stephen Breyer wrote in the 20-page majority opinion.

The lawsuit accused the big investment banks of conspiring to impose anti-competitive charges on prospective buyers and inflating share prices in the post-IPO aftermarket for some 900 initial public offerings.

The ruling was a major victory for the big investment banks, including Credit Suisse Group, JPMorgan Chase, Merrill Lynch and Morgan Stanley, which had appealed to the Supreme Court.

The Supreme Court's ruling said the underwriters should be immunised from such an antitrust lawsuit because the US Securities and Exchange Commission regulates the firms and the conduct at issue.

Mr Justice Breyer said that to permit antitrust lawsuits such as this one threatened serious securities-related harm.

A federal judge initially dismissed the class action lawsuit on the grounds that federal securities laws pre-empt federal and state antitrust laws, but the appeals court disagreed in reinstating the lawsuit.

It ruled there was no evidence that Congress intended to repeal the antitrust laws and immunise "tie-in" agreements on IPOs.

Other well-known firms involved included units of Bear Stearns, Citigroup, Fidelity Investments and Goldman Sachs Group.