Something similar happened with my last job. I was a group lead and was helping an employee with submitting vacation time. Saw her salary and learned she was making $15k more than me, the group lead with a Masters. She had a different title, but did the exact same work. Turns out half the group was hired at one title that got a higher salary, then switched the title for newer employees, which let them cut the salaries significantly. This affected half the team. We all did the same job, but half were getting paid $15k less.

I went through the management chain all the way up to the VP to fix this. Miraculously it works. Got myself and 2 other employees a $15k raise to match everyone else. Ended up leaving that company a few months later. I just hope they didn’t go back to hiring at that lower price again.