Although prior research on shareholder activism has highlighted how such activism can economically benefit the shareholders of targeted firms, recent studies also suggest that shareholder activism can economically disadvantage nonshareholder stakeholders, notably employees. Our study extends this research by exploring whether shareholder activism by institutional investors (i.e., institutional investor activism) can adversely affect employee health and safety through increased workplace injury and illness. Furthermore, deviating from the assumption that financially motivated institutional investor activists are homogeneous in their goals and preferences, we investigate whether the influence of institutional investor activism on employee health and safety hinges on the political ideology of the shareholder activist and of the board of the targeted firm. Using establishment-level data, we find that institutional investor activism adversely influences workplace injury and illness at targeted firms and that this influence is stronger for nonliberal shareholder activists and for firms with a nonliberal board. Our study contributes to shareholder activism research by highlighting how the political ideology of shareholder activists and boards affects the impact of shareholder activism on stakeholders and how shareholder activism can adversely affect the health and safety of employees. Furthermore, our paper also contributes to research on workplace safety and the management of employee relations and human capital resources by highlighting the detrimental effect of a firm’s ownership by investor activists on its employees and how the board’s political ideology may enable a firm to reduce this risk.