Unless someone is being paid over or under what they're worth, this isn't a problem.

If they are being paid under, then now is the right time for them to leave to an employer who rewards employees fairly.

If you're been paid over, then it's time you got your butt in gear and worked your ass off to prove to everyone your worth! :D

Personally I believe in 100% transparency across the board from day 1 (at Trak.io and all my previous companies). That way, situations like this can't arise, and new people coming in are unlikely to ask for misaligned salaries they know wouldn't stand up under peer review.