The move by Wal-Mart, the world's largest retailer, comes a day after Walgreen Co instituted a similar practice.

The U.S. government has struggled to roll out the Affordable Care Act, also known as Obamacare. A plethora of enrollment problems have affected the site's website, HealthCare.gov, since its October launch. Many insurance companies have said they are not getting accurate enrollee information required to process forms.

Wal-Mart said it will fill up to a 30-day supply of prescriptions through the end of January for customers who have enrolled in Obamacare, but do not have an ID yet from an insurer.

It was not immediately clear if Wal-Mart would seek reimbursement once customers obtain their Obamacare IDs, though Walgreen said it would do so.

A Wal-Mart representative was not immediately available to comment.