Deeply embedded protostellar jets are well known to be dominated by the emission of thermal electrons. Interestingly, in the last decades, negative spectral indices have been detected at centimeter wavelengths in some protostellar jets, indicating the presence of a non-thermal component. Detecting non-thermal emission implies the existence of relativistic particles interacting with magnetic fields, and therefore, the action of a mechanism able to efficiently accelerate them. In this talk I will discuss the conditions that need to be met in order to produce efficient particle acceleration in these low energy systems, based on the analysis of radio continuum images of two representative young stellar objects, obtained with the Karl G. Jansky Very Large Array.