Abstract: We explore, for the first time, neutral-current events at long-baseline  experiments to constrain vector and axial-vector neutrino non-standard interactions (NSI) with quarks. We leverage the flavor dependence of NSIs to perform an oscillation analysis in the neutral-current channel. We first introduce a framework to parametrize the effect of NSI on the cross section. Then, as an example, we analyze NOvA neutral-current data which provides significantly improved constraints on the axial-vector NSI parameters $\varepsilon_{\mu\mu}^A,~\varepsilon_{\tau\tau}^A$ and $\varepsilon_{e\mu}^A$. This is highly complementary to SNO. Additionally, we disfavor large values of the diagonal vectorial NSI $\varepsilon_{\mu\mu}^V$ and $\varepsilon_{\tau\tau}^V$ which originate from the LMA-Dark solution. We also highlight the complementarity between NSI searches at oscillation experiments using charged current and neutral current channels.