Programmer: We computer programmers at Mytheco are demanding raises to make our average salary comparable with that of the technical writers here who receive, on average, 20 percent more in salary and benefits than we do  This pay difference is unfair and intolerable  Mytheco executive: But many of the technical writers have worked for Mytheco longer than have many of the programmers
Since salary and benefits at Mytheco are directly tied to seniority, the 20 percent pay difference you mention is perfectly acceptable
whether the sorts of benefits an employee of Mytheco receives are tied to the salary of that employee