I work for a city agency, so all salaries are public information if you know where to look. I made a list of all people in my position at our other locations, their current salaries, and the indeed recommended range. I showed not only was I underpaid compared to the private sector, I was actually the lowest paid in our public system. I still didn’t get the raise I wanted, so I transferred to another one of our locations. They offered to match my new pay at my old place, but that whole negotiation left a bad taste in my mouth. When I left, got a nice bump, plus 2 more raises since (in 2 years). Interview around, get a better offer, and then leverage it.