I don't know on what basis you raised your query with reference to those who are drawing a salary of more than Rs. 24,000. Even in the definition of the term "employee" under the Act, there is no reference to the amount of salary or wages drawn. Therefore, the very first point is that once employment in a particular industry is brought under the schedule of the MW Act, 1948 by the appropriate Government and minimum rates of wages are fixed, the employer has to simply implement it.
Secondly, the minimum wages fixed are common to all employees, including juniors and seniors in terms of service. When a particular state government deems it necessary to grant some additional benefits to employees based on their length of service, it is a welcome decision. Therefore, when such a new component is introduced by the government into the structure of the existing minimum wages, it automatically falls under the inclusive components of the term "wages" under the Act.
Therefore, you have to pay the so-called "SSA" to all categories of employees if their industry wages minus the excluded items [under section 2(h)] fall short of the minimum wages fixed.