OK, generally, an employer has the legal authority to delegate work as it sees fit, and the employee has no powers, rights or authorities to change things unileterally. Not as provided for by law - this is so with some limited exceptions I will describe below.
However, if the employee's contract (written) with the employer actually includes terms defining how this will be done, the work delegation, that would mean the 2 parties agreed and can rely on that contract term - it can be enforced in court. This would be unusual, however.
If there is no such contract then there is no basis on which the employer has lost its rights to delegate as it sees fit - even if the employee(s) think it is being unfair. That being said, if the workload is being unfairly distributed for some narrow ILLEGAL reasons - then the employee being discriminated against - or someone else witnessing it - can notify the upper management to hope it gets corrected and if not, he can file a claim for that illegal discrimination
with the EEOC
. For instance, if the unfair distribution is because he is male, and the females don't suffer the same unfair workload, that can be illegal workplace discrimination based on gender. Or, it could be based on religious beliefs, race, ethnicity, etc. You can read more on that at http://www.eeoc.gov/laws/types/index.cfm
So, in sum, unfair workplace delegation of workload is not illegal generally, and is only actionable if:
1) Parties had a contract terms making it contrary to the employment agreement
2) The basis for the unfair workload is an illegally discriminatory one, such as those categories covered by the EEOC.
I hope this helps! My goal is to provide you with excellent and accurate service – if you feel you have gotten anything less, please reply back, I am happy to address follow-up questions. Kindly rate me "excellent" when you are done. I look forward to assisting you in the future, should you have legal questions.