Final answer:
The statement that is not true about trade zones, specifically SEZs, is the presence of non-unionized labor, as SEZs can have unionized workers despite tax benefits aimed at encouraging economic activity.
Step-by-step explanation:
The question 'which of the following is not true about trade zones' pertains to characteristics of trade zones, specifically special economic zones (SEZs). Of the listed options - tax free zones, no import taxes, lack of export taxes, and non-unionized labor - the one that is not necessarily true about SEZs is 'non-unionized labor.' While SEZs generally offer tax benefits to encourage economic activity, including being tax free zones with no import or export taxes, they do not inherently ban unionized labor. In the context of international trade and special economic zones, the lack of wide-ranging trade restrictions like tariffs or quotas is designed to stimulate economic activity within these designated zones.