Duty of post lower than workers

The employee has to do such work without creating problems to have mental peace and represent to Union.  It is Govt that is wasting money and time by giving higher salaries with inferior duties.   However, attending menial jobs can be politely denied by objecting in the form of a polite letter to the immediate boss

Who is the employer, Government or private?  What is the kind of estblishment, is it a factory, an office or any other type?  What is the normal type of job?  What is allegedly the lower type of job? Details are necessary to give an opinion.

What are the facts? What is the context?

even a govt employee cannot refuse duty even if tenable by lower post.

The query is without full facts.

Why "even a govt employee"?   The answer to the question has nothing to do with "govt or private" until the other particulars are missing. Very often a promotion to a higher post only means higher emoluments or higher status with no change in the nature of work. Hence without details the question cannot be answered.