Most large companies generate what’s called a “compa ratio” which means your salary compared to the midpoint for your role. As an example say for your position at your level the pay is 0-200k a year, if you got 100k a year you’d be at 1.0. 90k would be .9, etc.
Most companies have HR that has to share this or will if asked. It’s a good way to see if minorities are underpaid as well as long-term workers vs newly hired. (Nothing against newly hired people, just long term employees get screwed)
If your company doesn’t have it, ask. Get your coworkers to ask. It’s a start if nothing else and a great data point if you want to unionize to show WHY they’re all getting screwed over today. Plus sharing .94 vs [exact pay] can be more comfortable for those more conservative about talking pay to get them to realize why it matters.