Now that their agreement with the White House has ended, U.S. retail giants Walmart and Kroger have now raised the price of an on-demand COVID-19 rapid test kit. The two retailers announced Tuesday that they would be returning the price of BinaxNOW antigen self-kits to their regular rate.

The retailers and the kit's manufacturer previously reached a 100-day agreement with the Biden administration for the sale of the kits at $14 per unit. Walmart said it will now be increasing the price of the kits to $20, while Kroger said it would be selling them for $24 per unit.

The increase in prices comes as demand for the rapid test kits continues to be at elevated levels as the threat of the COVID-19 pandemic remains. Cases have recently increased throughout the country as the more contagious Omicron variant of the coronavirus continues to spread.

The deal with Abbott Laboratories to sell their kits at cost, which was made on Sept. 9, officially ended in mid-December. Despite the agreement ending, Walmart continued to sell the kits at the same price throughout the holiday season.

Walmart said that it had prolonged selling the kits at lower prices for as long as possible, but it would now be going back to its retail pricing. Kroger also made a similar announcement stating that the pricing program it had agreed to had long phased out.

Prior to the announcement of the price increase, stocks of BinaxNow at the stores were in low supply. The company said, "significant demand" had resulted in it going out of stock.

Holiday gatherings, less stringent mask-wearing and social distancing rules, as well as the spread of the highly contagious Omicron variant have fueled a rise in demand for COVID-19 testing, making the kits difficult to locate and stay in stock.

Amazon also took part in the deal and sold the kits at the cost of $14 per unit. However, it has been a while since the kits were made available for sale on the company's website. Amazon has not yet announced if it would be able to get more supply or if it would be increasing its prices as well.

During the holidays, U.S. President Joe Biden had outlined a plan to provide as many as 500 million citizens free COVID-19 rapid tests. Biden made the plan following an overnight surge in new COVID-19 cases.

Biden is reportedly working on new deals with manufacturers to bring down prices of essential goods such as rapid COVID-19 tests. The president has yet to provide any updates on his previous plan of providing free tests.