  Emerging scholarship suggests that the EU legal concept of direct
discrimination - where a person is given different treatment on grounds of a
protected characteristic - may apply to various algorithmic decision-making
contexts. This has important implications: unlike indirect discrimination,
there is generally no 'objective justification' stage in the direct
discrimination framework, which means that the deployment of directly
discriminatory algorithms will usually be unlawful per se. In this paper, we
focus on the most likely candidate for direct discrimination in the algorithmic
context, termed inherent direct discrimination, where a proxy is inextricably
linked to a protected characteristic. We draw on computer science literature to
suggest that, in the algorithmic context, 'treatment on the grounds of' needs
to be understood in terms of two steps: proxy capacity and proxy use. Only
where both elements can be made out can direct discrimination be said to be `on
grounds of' a protected characteristic. We analyse the legal conditions of our
proposed proxy capacity and proxy use tests. Based on this analysis, we discuss
technical approaches and metrics that could be developed or applied to identify
inherent direct discrimination in algorithmic decision-making.
