Wal-Mart Stores Inc. is cutting health insurance for another 30,000 part-time workers and raising premiums for its other employees, as U.S. corporations push to contain costs in the wake of the federal health-care law.

Autumn is typically when U.S. companies unveil changes to employee insurance plans. This is the first such enrollment period since employers could assess the full financial impact of the federal health-care overhaul, and it is a key moment as companies work to lower their spending ahead of looming taxes on...