Ras pathway signaling plays a critical role in cell growth control and is often upregulated in human cancer. The Raf kinases selectively interact with GTP-bound Ras and are important effectors of Ras signaling, functioning as the initiating kinases in the ERK cascade. Here, we identify a route for the phospho-inhibition of Ras/Raf/MEK/ERK pathway signaling that is mediated by the stress-activated JNK cascade. We find that key Ras pathway components, the RasGEF Sos1 and the Rafs, are phosphorylated on multiple S/TP sites in response to JNK activation and that the hyperphosphorylation of these sites renders the Rafs and Sos1 unresponsive to upstream signals. This phospho-regulatory circuit is engaged by cancer therapeutics, such as rigosertib and paclitaxel/Taxol, that activate JNK through mitotic and oxidative stress as well as by physiological regulators of the JNK cascade and may function as a signaling checkpoint to suppress the Ras pathway during conditions of cellular stress. Display omitted •Route for the phospho-inhibition of Ras pathway signaling mediated by JNK cascade•Stress-induced S/TP phosphorylation inhibits the function of Sos1 and the Rafs•S/TP phospho-regulatory circuit may act as a stress-induced signaling checkpoint•S/TP circuit engaged by cancer drugs that activate JNK via mitotic/oxidative stress The Ras pathway is an important cellular signal transduction pathway frequently activated in human cancer. Ritt et al. identify a route for the phospho-inhibition of key Ras pathway components, Sos1 and the Rafs, that is mediated by JNK cascade activation and may function as a stress-induced signaling checkpoint.