  We study the experimental constraints on strongly interacting vector-fermions
compatible with the relaxion mechanism and investigate any possible tuning. The
focus is on a minimal model and low confinement scale. More precisely, we study
bounds from electroweak precision tests, Higgs decay, Big Bang nucleosynthesis
and direct collider searches. The effect of these new fermions on vacuum
stability is also investigated. Combining our bounds, we show that the relaxion
mechanism becomes increasingly constrained and fine-tuned as the confinement
scale decreases. For example, a confinement scale of a few tens of MeVs would
require tuning at the percent level.
