Traditionally, the Thai statutes regarding income tax are dismissed up to a certain wealth status - meaning that the working classes/working poor are exempt, especially true when such income is dispersed/traded in cash and not recorded. This is the manner in which it should be practiced everywhere.....of course, it's not.
There are some particular circles that might suggest that taxing the everyday struggling working/labour classes income is a bit barbaric and accomplishes nothing for the real working economies.