Low-energy signatures of quantum gravity might appear as small violations of fundamental symmetries, such as Lorentz and CPT invariance. While experiments have placed stringent constraints on many effective interactions involving stable particles, investigating effects in confined and unstable particles presents additional challenges. Notably, relatively few studies have probed the Lorentz and CPT properties of partons. I will introduce an EFT framework that facilitates the study of quark-sector violations in perturbative hadronic processes, encompassing deep inelastic scattering and the Drell-Yan process. I will then discuss how this framework formed a foundation for a recent search performed by the ZEUS Collaboration, resulting in several first constraints on light-quark sector Lorentz and CPT violation.