Dissident shareholders are pressing once more for the media mogul Rupert Murdoch to step down as chairman of News Corporation. Shareholders from the US, UK and Canada filed a resolution on Tuesday, calling for News Corp to appoint an independent chairman. A similar resolution attracted strong support at the media company's annual shareholder meeting last year. The proposal was introduced by Christian Brothers Investment Services (CBIS), which manages $4.6bn for Catholic institutions worldwide. It is backed by the UK's Local Authority Pension Fund Forum, with assets of £115bn ($178.9bn), and British Columbia Investment Management Corporation, one of Canada's largest institutional investors. In a separate resolution, Nathan Cummings Foundation, an ethical investment group, has called on News Corp to end the dual-class share structure that allows the Murdoch family to control its media empire despite owning a minority of shares.