Demands on hedge funds to lift the lid on their secret holdings in companies are growing as executives fight back against activists while regulators and traditional investors worry about orderly markets.

The latest pressure comes in the US, where CSX, the rail operator, is suing The Children’s Investment Fund and 3G Capital Partners, claiming they used derivatives as part of a plan to “influence control of CSX by acquiring a large stake in CSX while evading the reporting requirements of the securities laws”.