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We study the $\mu\to e$ conversion process in nuclear targets arising inmodels of axion-like particles (ALPs) with hadronic and charged lepton flavorviolating (CLFV) interactions. Contributions to this process generally fallinto two categories: spin-independent (SI) and spin-dependent (SD). While theSI contribution can be generated by a dipole operator through purely leptonicALP interactions, the SD contribution can also be present through ALP-quarkinteractions at tree-level. It is naively anticipated that the SI contributionwould be dominant due to its coherent enhancement. In this $\textit{letter}$,we show that is not generically the case; in particular, for naturally-sizedALP couplings to quarks of order $\sim\!m_q/f_a$, the SD interaction induced byALP-$\pi^0$ mixing turns out to be the leading contribution to $\mu\to e$conversion. Intuitively, this stems from the suppressed dipole contribution bythe QED one-loop factor which counters the effect of SI coherent enhancement.Our study highlights the importance of $\mu\to e$ conversion searches inexploring the parameter space of generic ALP models, and demonstrates thecompetitiveness of these searches in probing the CLFV ALP parameter space inthe heavy mass range of $m_a\gtrsim m_{\mu}$.

ALP contributions to $\mu\to e$ conversion