On May 1, 2018, the U.S. Environmental Protection Agency (EPA) published a proposed rule seeking comments in response to a petition requesting the revision of the EPA's regulatory definition of volatile organic compounds (VOC) to exempt cis-1,1,1,4,4,4-hexafluorobut-2-ene (also known as HFO-1336mzz-Z; CAS number 692-49-9). The EPA is now taking final action to revise the regulatory definition of VOC under the Clean Air Act (CAA). This final action adds HFO-1336mzz-Z to the list of compounds excluded from the regulatory definition of VOC on the basis that this compound makes a negligible contribution to tropospheric ozone (O3) formation.