The air traffic control centers of Brazil are known by the acronym CIND****ACTA, or "Centro Integrado de Defesa Aérea e Controle de Tráfego Aéreo (Integrated Air Traffic Control and Air Defense Center). Four CIND****ACTAs are in operation, located in four cities and each responsible for different regions of Brazil's airspace. The use of military air traffic controllers for civilian traffic is not unusual. In the US, the Federal Aviation Administration (FAA) operates a wholly parallel system with that of the US Air Force and NORAD. This is also the case of Eurocontrol and each of its member nations' air defense systems. Brazil's use of an integrated command poses some unique challenges to the government. As members of the military, controllers are not allowed to form unions (such as the case of NATCA in the US) or to strike.