A leading shareholder advisory group Tuesday urged JPMorgan Chase investors to end chief executive Jamie Dimon\'s tenure as chairman and fire a majority of the company\'s board after a $6.2 billion trading loss. Glass Lewis became the second major proxy advisor in recent days to endorse splitting the chairman and chief executive roles at JPMorgan in the wake of the bank\'s \"London whale\" derivatives debacle. ISS Proxy Advisory Services called for that action last week. CalPERS, which manages California government retirees accounts, also said Tuesday that it would vote to split the banks\' chairman and chief executive roles. The pressure came ahead of JPMorgan\'s annual meeting May 21 as questions about Dimon\'s fate hang over Wall Street. After leading JPMorgan through the 2008 financial crisis in comparatively good shape, Dimon\'s star has dimmed after the multi-billion-dollar loss in early 2012 by a London-based unit trading complex derivatives for the bank\'s own book. Glass Lewis said that separating the chairman from a role as a corporate officer \"is almost always a positive change\" because it curbs conflicts of interest, promotes oversight of risk and generally better serves shareholder needs. But Glass Lewis also took a swipe at Dimon over the London trading debacle. \"Given the massive trading losses at the company, we believe shareholders would benefit from independent board leadership to prevent such loss of shareholder value in the future,\" it said in a statement. Glass Lewis also urged shareholders to fire six of JPMorgan\'s 11 independent directors, specifically the members of the audit and risk policy committees. Audit committee members James Bell, Crandall Bowles and Laban Jackson \"have not satisfactorily performed their duties,\" it said. They should have done more to ensure \"that the bank\'s traders cannot obfuscate the values of their positions with as much ease as evidently occurred in the London whale matter,\" Glass Lewis said. Similarly, Glass Lewis faulted risk committee members David Cote, James Crown and Ellen Futter for not seeking more information on the problem accounts and for not asking \"sufficiently probing questions of management at committee meetings.\" The risk committee was \"likely too willing to trust senior management\'s risk oversight\" and did not have adequate reviews in place, Glass Lewis said. JPMorgan\'s board has offered a strong defense of keeping Dimon in both posts, pointing to the bank\'s huge financial success under Dimon in comparison with other banks. But billionaire Warren Buffett, who heads investment giant Berkshire Hathaway, said he supports Dimon in both roles. \"I\'m 100 percent for Jamie. I couldn\'t think of a better chairman,\" he told Bloomberg TV on Friday. A similar proposal in 2012 to split the chairman and chief executive roles received 40 percent of the shareholder vote last year. That vote came days after the initial London losses were disclosed, but before their huge size was known and a damning US Senate report on JPMorgan\'s poor oversight was released. JPMorgan Chase shares gained 2.0 percent to $49.14 on Tuesday, and were up 17.6 percent from one year ago.