Protein-coding genes undergo a wide array of regulatory interactions with factors that engage non-coding regions. Open reading frames (ORFs), in contrast, are thought to be constrained by coding function, precluding a major role in gene regulation. Here, we explore Piwi-interacting (pi)RNA-mediated transgene silencing in C. elegans and show that marked differences in the sensitivity to piRNA silencing map to the endogenous sequences within transgene ORFs. Artificially increasing piRNA targeting within the ORF of a resistant transgene can lead to a partial yet stable reduction in expression, revealing that piRNAs not only silence but can also “tune” gene expression. Our findings support a model that involves a temporal element to mRNA regulation by germline Argonautes, likely prior to translation, and suggest that piRNAs afford incremental control of germline mRNA expression by targeting the body of the mRNA, including the coding region. Display omitted •C. elegans germline mRNAs differ in sensitivity to piRNA targeting•piRNA targeting of coding regions provides incremental control of gene expression•Piwi Argonaute surveillance occurs upstream of nonsense-mediated decay•Model, piRNAs scan mRNAs within perinuclear nuage prior to translation initiation Some C. elegans transgenes resist piRNA silencing. Seth et al. map resistance to endogenous sequences within transgenes and show that artificially increasing piRNA targeting can incrementally reduce expression without silencing. Their findings identify coding regions as part of a rich piRNA regulatory landscape within perinuclear nuage.