Codes of labour practice implemented by corporate buyers in their global production networks are one dimension of corporate social responsibility (CSR). Research indicates the benefits of codes for workers are limited and they fail to reach the most vulnerable workers, particularly those employed by labour contractors who face the worst employment conditions. This contribution argues that the commercial dynamics of global production networks provides an opening for civil society organizations to pressure for codes, but simultaneously drives the use of a vulnerable and insecure workforce that is the 'Achilles Heel' of codes. Whilst codes have a role to play, inherent tensions underpinned by a commercial logic mean they should only ever be viewed as one strand in broader strategies that address the rights of the most vulnerable workers in global production.