"Most companies are not under any significant pressure to increase their salary budgets in the near term," says Laura Sejen, managing director, human capital and benefits at Willis Towers Watson. "Companies are relying more on variable pay, such as annual incentives and discretionary bonuses, to recognize and reward their best performers. At the same time, they are rewarding star performers with significantly larger increases while granting minimal increases to their weakest performers."

For those exempt workers who received the highest performance ratings this year, employers granted them a 4.5 percent raise on average — about 73 percent larger than the 2.6 percent increase given to employees receiving an average rating.

Those workers with below-average performance ratings received salary increases of 1 percent on average.

Annual performance bonuses, typically paid for meeting company and employee performance goals, will either hold steady or decline slightly in 2018 for most employee groups.

Exempt employees are projected to receive bonuses that average 10.5 percent of salary, roughly the same amount companies budgeted for this year.

Discretionary bonuses, generally paid for special projects or one-time achievements, will continue hold relatively steady – last year, 75 percent of companies paid discretionary bonuses, and in 2015, 72 percent did so.

"Employers are rethinking how to administer limited salary budgets," says said Sandra McLellan, rewards practice leader, North America at Willis Towers Watson.

"Some organizations are moving away from differentiating increases based on an employee's previous year's performance altogether while others are focusing on rewarding employees for skills development," McLellan says. "So while organizations may be forecasting three percent increases, the landscape of how and when they are giving increases varies considerably."