Nice idea but in practice will likely result in other discrimination.

People should not be paid differently because of their gender or ethnicity. BUT there are often factors associated with gender or ethnicity that affect job capability - times of day a person prefers to work, how long a day they will work, how often they will take extended leave from work, how long they stay with same employer.

All those affect an employee's value to an employer, and people should be paid differently because of it.

But this law produces a race to the bottom, where you either discriminate against people who are willing or able to work longer hours, without taking leave, and stay with the employer by paying others more than they are worth, or you push everyone to a lower wage and discourage people from working harder.