From Insider:

If you suspect you're being paid less than same-level colleagues, do some research before approaching your boss.

Business Insider's comprehensive guide on how to ask for a raise includes tips for nding out what you're worth in the market.
Their guide also features scripts for conversations with colleagues, with your manager, and with your HR department.
The issue of unfair compensation is especially relevant today, now that employees are more willing to share their salaries and employers are more focused on narrowing their gender pay gaps.