Can you come up with an objective definition of "merit" that the company can't game in order to fire the most active union members and break the whole thing apa

Can you come up with an objective definition of "merit" that the company can't game in order to fire the most active union members and break the whole thing apart? IME seniority and political patronage is basically how a lot (if not most) companies promote too - under the guise of being purely concerned about objective performance of course.