My colleagues and I recently discovered that new hires for our position are being recruited with a salary that is 20% higher. Thus they are being paid more than us even though we have as much as 5 more years of experience in the same position. Other hires of equal seniority to us, but with different specializations, are also receiving this 20% higher salary.
Are there legal grounds for arguing that we deserve equal pay? Is it illegal to pay different employees different amounts for the same work, if the difference is not based on a protected attribute like gender or race? Could we argue that there is a "standard wage" that we are not receiving?