ANSI Standards for Electricity Metering C12
The American National Standard Institute, Inc. (ANSI) is not a government agency. It's standards do not have force of law so in once sense compliance is voluntary. However, in the case of the C12 family of metering standards, many state public service commissions make utility compliance with C12 a requirement. ANSI doesn't actually generate any standards itself. For each family of standards it appoints a "secretariat" which oversees the standards process. For C12, NEMA (National Electrical Manufacturers Association) is the secretariat.
NEMA organizes committees to propose and review standards. For C12 there is a "Main" committee which must approve all actions and a number of subcommittees where actual standards development and review takes place. Each standard is assigned to a subcommittee. Here's some useful information.