CVS health officials say Walmart pharmacies are likely to leave its caremark network if the two companies can't agree on pricing.
Those consumers with CVS drug benefits and medicaid with CVS drug coverage will be affected if a split happened.
This means prescriptions filled at a Walmart pharmacy will not be eligible for coverage by their CVS drug plans.
Walmart is one of the largest pharmacy chains in the U.S. with about 4,600 locations.
CVS says it has asked Walmart to stay in its network and continue to fill prescriptions through April 30.
Sam's Club is expected to remain in the CVS caremark network as well as medicare plans.