Most labor contracts have specific wage increments built into their language.
Increases in salary and fringe benefits can be spelled out on a percentage or lump-sum basis or an hourly increment, as appropriate. In order to reward performance that is above average, many contracts, especially those involving professional personnel, have pools of money to be distributed on the basis of merit. These may be one-shot bonuses or permanent additions to the employee's base salary. Whoever is in charge of deciding how this pool of money is to be distributed is in a no-win situation. Disproportionately large sums to certain individuals will always bring cries of favoritism from those less rewarded.