Wal-Mart Stores Inc. (WMT) announced new initiatives on Thursday to recognize performance and service among its employees, including a bonus plan to recognize store workers who have been with the company for 20 years or more.

The company also said it awarded more than $529.8 million in bonuses to 813,759 hourly associates from its U.S. Wal-Mart and Sam's Club stores on Thursday, a day it is calling Associate Celebration Day.

The world's largest retailer said it employs more than 13,400 hourly workers with 20 years or more of service.

Store associates and assistant managers with 20 or more years of service will get an extra week of pay under the new Servant Leadership bonus plan.

Wal-Mart also said it would reward employees who provide outstanding customer service with a cash bonus. That plan will begin in mid-summer.

Union-backed groups like WakeUpWalMart.com and Wal-Mart Watch have launched grass-roots campaigns to draw attention to what they regard as poverty-level wages, inadequate health-care benefits and other issues at Wal-Mart.

All Wal-Mart hourly full- and part-time store employees are eligible for annual "My$hare" bonuses, which are allocated based on store performance. The company said these bonuses will now be distributed quarterly, rather than annually, so that workers are rewarded more frequently.

Wal-Mart, which is based in Bentonville, Arkansas, was not available to provide additional comments about the plan on Thursday morning.