Investors in JP Morgan have been urged to vote in favour of splitting the role of chief executive and chair at America’s largest bank, amid concerns over the power wielded by its billionaire boss Jamie Dimon.

ISS and Glass Lewis, which issue advice to some of the world’s biggest fund managers on how to vote at annual investor meetings, have thrown their weight behind a shareholder resolution that would ensure two separate people hold the office of chair and chief executive “as soon as possible”. Investors are due to vote on the resolution at the bank’s annual general meeting on 19 May.

Dimon, who is worth an estimated $2.6bn (£1.9bn), has held the dual role for two decades. Holding the two most senior roles in a company is widely frowned upon in corporate governance circles, particularly in Europe, but not banned.

“The size and complexity of JP Morgan suggests that it is difficult for any one person to run both the company and the board,” ISS said in its shareholder report.

“The board is responsible for overseeing management and instilling accountability, and conflicts of interest may arise when one person holds both the chairman and CEO positions, thereby leading both the management team and the board which oversees it,” ISS said. “Effective board oversight may be enhanced by independent leadership.”

Glass Lewis said that an independent chair would be “better able to oversee the executives of the company and set a pro-shareholder agenda.”

The guidance has put the proxy advisers on a collision course with Dimon, who has held the chief executive and chair roles at JP Morgan since 2005 and 2006, respectively.

The two firms have long been in Dimon’s crosshairs. He has accused Glass Lewis and ISS of having too much sway over shareholders, particularly when it comes to social and environmental issues. Dimon – seen as the world’s most powerful banker – has also taken a patriotic stance, highlighting that neither firm is American-owned. Glass Lewis and ISS are owned by Canadian and German firms, respectively.

The battle has also made its way to the White House. Trump in December signed an executive order aimed at reining in Glass Lewis and ISS, which he claimed were using their power “to advance and prioritise radical politically motivated agendas”.

JP Morgan (JPM) has since shunned their use at its asset management arm, which is instead using its own internal AI-powered platform to help decide how to vote at the annual general meetings of companies held in its portfolios, according to the Wall Street Journal.

JP Morgan is urging investors to oppose the shareholder proposal – brought by an individual retail investor – to split the chair and chief executive roles, and has written public letters to Glass Lewis and ISS urging them to overturn their recommendations.

The bank said there was no evidence that companies with independent chairs performed any better than rivals, adding that any suggestions an independent chair would be better at overseeing executives and setting a pro-shareholder agenda “omits any reference to or consideration of JPM’s strong record of absolute and relative outperformance versus peers”.

The proposal revives a long-running debate over whether board independence is compromised by combining the roles, which are typically split at companies across Europe.

While JP Morgan’s board has said they intend to separate the two roles after Dimon steps down, ISS said there was “a clear possibility” he would stay on as chair, meaning the effectiveness of any lead independent board member would be overshadowed.

The bank said in its correspondence with Glass Lewis that the proxy adviser was looking to “undercut the flexibility the JPM board needs to design a leadership structure that enables orderly transition during management succession events, which does not promote shareholders’ interest”.

The bank said the current leadership structure “has overseen long-term, strong financial performance and continued, meaningful progress against key initiatives and effective execution on strategic priorities. “We believe that these results are tangible evidence of the board’s commitment to shareholder interests.”

A spokesperson for JP Morgan said the bank did not have any further comment.