Sports Direct is set for a showdown with a powerful group of investors worth £14.5tn ($19.2tn) who will call for an independent review of the retailer's corporate governance at its annual meeting in September.

It is the first time that the newly formed The Investor Forum, which represents huge asset management groups such as BlackRock and Allianz Global Investors, has publicly criticised a company since it was launched almost two years ago.

The move highlights the growing frustration between shareholders in the scandal-hit firm and its billionaire founder Mike Ashley, who owns a 55% stake in the business.

The Investor Forum will call for a report to "cover all aspects of corporate governance across the business, not only employment practices" at the firm's annual meeting on 7 September.

The investor body says it represents 27% of the firm's independent shareholders.

The Investor Forum executive director Andy Griffiths said: "It is highly unusual for the Investor Forum to consider it necessary to make public their concerns and recommendations in this way. We do not take this step lightly, but we have not received an appropriate level of commitment to respond to investor concerns."

A number of Sports Direct investors have warned they plan to oppose the re-election of the firm's chairman Keith Hellawell and other senior directors at the company's annual meeting due to a lack of independent leadership.

The growing row ‎follows damaging revelations about working conditions at Sports Direct, which MPs in June labelled "Victorian practices". Reports found that staff at its Derbyshire warehouse were harangued for not working fast enough, while long queues for staff searches after a shift sometimes meant workers earned below the minimum wage.

The Local Authority Pension Fund Forum (LAPFF) said this week it would support trade union plans to begin an investigation into Sports Direct's working conditions.

Legal & General Investment Management, one of the biggest single investors‎ in blue-chip UK companies, has voted against the Hellawell, at the last two years annual meetings. Pirc, the investment consultancy, has also urged shareholders to remove Mr Hellawell, who it said "failed to show leadership in a critical period for the company".

The consultancy has also called for the removal of Mr Ashley citing concerns about his influence over other board members.

The Financial Times also reported earlier this week that a company owned by Mr Ashley's brother is involved in distributing products sold by Sports Direct, while in January his daughter's 26-year boyfriend was put in charge of the group's vast property portfolio.

Sports Direct offered no comment.