ABOVE: uBiome is headquartered in San Francisco

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The Federal Bureau of Investigation is looking into biotech startup uBiome for miscoding financial compensation to doctors prescribing their products and over-billing health insurance companies for its home testing kits for human gut and vaginal microbiomes, reports STAT.

Agents from the Federal Bureau of Investigation (FBI) showed up on April 26 at the startup’s headquarters in San Francisco, California, for “court-authorized law enforcement activity,” an FBI spokesperson writes in a statement to CNBC. Some employees of the company were told to stay home from work on Friday, a person familiar with the matter tells CNBC. A uBiome spokesperson tells The Wall Street Journal, “We are cooperating fully with federal authorities on this matter.”

In recent months, three people say to CNBCthat uBiome has repeatedly charged patients’ insurance plans twice for the same test. The health insurance company Anthem has flagged uBiome internally for its over-billing practices, two people familiar with the matter tell CNBC. Other insurance companies examining the company’s billing practices include Aetna and Cambia Health Solutions, according to sources who spoke to The Wall Street Journal. The California Department of Insurance is also investigating the company, the Journal reports.

Last year, the company reported raising $83 million in venture capital funding from OS Fund and Y Combinator, according to the The Wall Street Journal.