Wage discrimination is known to be a form of discrimination in which the amount of money which employers of labour pay to workers or employees for doing the same job varies. In essence, workers earn different pay for performing similar work or task which can be paid to them, hourly or daily. Thus, this can be as a result of race, disability, gender, religion, sex and so on.
Oftentimes it is "removing barriers to trade" that motivates countries to join regional trade blocs, since members of such "blocks" have completely free trade with one another.