There is a classic HBR article by Frederick Herzberg ( http://hbr.org/2003/01/one-more-time-how-do-you-motivate-employees/ar/1 ) in which he describes a distinction between things that motivate employees and things that cause dissatisfaction. Guess what... salary is one of the dissatisfiers. Although people certainly appreciate getting paid for their work, their salary does not cause them to jump out of bed in the morning, eager to get back to work. On the other hand, if there is a sense that a given salary is not fair, an unhappy employee is almost sure to follow.
Fairness, or justice, comes in three varieties:
1. I get my fair share
2. Share are not equal but I understand the rationale
3. Shares are not equal, and I intend to get even
Since any rationalization of your compensation policy would probably necessitate reductions in salary for some of your employees, or at least no increases until things evened out, there would seem to be some risk of generating unhappiness and/or anger, because any takeaway is perceived as a violation of "I get my fair share". It may well be a great investment to have expert help from an objective third party, who could give you a basis for explaining the change, thereby achieving fairness via point #2. In any case, it will be important to be thoughtful in planning how to introduce a change such as this. Transparency, respect, and abundant two-way communication should help.