(Bloomberg) -- The Biden administration on Wednesday will begin accepting orders for free at-home Covid-19 tests, the latest government response to a record number of infections.

Each U.S. household that asks for tests via CovidTests.gov, or by phone, will receive four kits drawn from a 500 million-test order approved by President Joe Biden in December. 

The administration expects the tests to initially be delivered by the U.S. Postal Service in seven to 12 days, though shipping may move faster as the program ramps up. The administration believes the website and Postal Service are prepared to meet demand, officials said.

The move comes as the fast-spreading omicron variant has caused demand for tests to spike, leaving many Americans facing long lines at testing centers and empty shelves at stores selling at-home kits.

The administration has signed contracts for 420 million tests with four companies that had large stockpiles of unused tests available for quick distribution. Contracts for the remaining 80 million tests will be finalized in the coming days, one official said. The program will cost an estimated $4 billion for the 500 million tests, the official said.

The tests are just the first tranche being purchased by the federal government. Biden said Thursday that his administration will buy another 500 million tests. He pledged that the administration would “continue to work with the retailers and and online retailers to increase availability.”

The test purchases are among the steps the White House is taking to expand test availability. Federal testing sites have expanded around the country, and the administration is requiring private health insurers to pay for up to eight tests a month beginning Saturday.

An Economist/YouGov poll released Thursday found that 53% of American said they would request free tests from the federal government if they were available, while another 20% said they were unsure. The percentages of Democrats and vaccinated Americans who said they would request tests were even higher -- 72% and 63%, respectively.

The poll also found that among the one-in-five Americans who have acquired at-home tests, nearly half said they had difficult acquiring them.

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