The Federal Trade Commission has warned 10 companies to stop making health claims about treating and preventing the coronavirus or pitching business opportunities amid the pandemic, the agency announced on Friday.

The group of letters represent the first time the F.T.C. has issued warnings about claims of potential earnings related to the economic fallout from the pandemic. The commission and the Food and Drug Administration have previously sent warning letters about unapproved health products related to the coronavirus.

There currently are no products that are scientifically proven to treat or prevent the virus, according to the F.D.A.

In the recent letters, the trade commission targeted so-called multilevel marketers, which distribute products or services through networks of salespeople who are not employees of the company and who do not receive a salary or wage. It warned the companies that false or misleading earnings claims are a violation of federal law.