US Bancorp Piper Jaffray faces a $20m (€20m) claim from a former corporate client and a possible government investigation after the National Association of Securities Dealers (NASD) ruled that the US bank used bullying tactics in a bid to win underwriting business.

Scott Beardsley, a senior banker in the firm's biopharmaceutical investment banking team, made threats that 'Piper would discontinue research coverage and stop making a market in the company's stock if it did not select Piper as lead underwriter for a planned secondary offering,' the NASD said in a statement.