(NewsNation Now) — With the highly contagious omicron variant sweeping the nation, retailers are now limiting the number of at-home COVID-19 tests customers can buy due to high demand.

Walgreens imposed a purchase limit on at-home COVID-19 testing products across its 9,000-plus stores and online. The company said customers will now be limited to just four items per in-store and online purchase “in an effort to help improve inventory.”

A Walmart spokesperson said inventory is “strong but limited” for online orders. Customers purchasing kits online are limited to eight per order. Additionally, each store may set its own limits based on local inventory.

CVS Health is following suit. The company said it continues to work to provide its customers with a limit of six at-home COVID tests.

“To ensure equitable access to tests both in-store and digitally, we’ve added a limit of six test kits per purchase,” the company said. “Due to a recent surge in demand, and to retain community-based access to tests in our stores, there may be temporary out-of-stocks for these products on CVS.com.”

Amazon is also being mindful of its product limits. An Amazon spokesperson told NewsNation it is allowing “third party sellers to set their own product quantity limits for COVID-19 tests available on Amazon.com.” The company said it is working with its selling partners to secure additional test inventory.

The company says it sets its own quantity limit for the Amazon COVID-19 Test Collection Kit.

On Tuesday, President Joe Biden pledged a half-billion free COVID test kits to counter the spread of the virus. The rapid tests will be shipped to Americans starting in January.