The Federal Trade Commission (FTC) is cracking down on companies that are offering unproven cures or treatments for the coronavirus.

The FTC, which enforces consumer protection laws against fraud and deceptive business practices, issued 20 warning letters last week to companies and individuals for allegedly making “unsubstantiated” claims that their products could prevent or treat the disease.

The agency sent warning letters to at least seven companies that said, “We have determined that you are unlawfully advertising that certain products or services treat or prevent Coronavirus Disease 2019,” and demand the companies “immediately cease making claims that are not supported by competent and reliable scientific evidence.”

The companies have 48 hours to respond to the FTC. In most cases, alleged offenders quickly comply by removing the marketing claims. But if they fail to do so, the FTC may file lawsuits in federal court, which could lead to court-ordered injunctions as well as financial penalties.

Throughout the coronavirus pandemic, medical experts have warned Americans to watch out for fake treatments and purported “cures.”  The FTC said it has issued more than 330 warning letters since the beginning of the pandemic as part of what it calls an “unprecedented” effort to “flatten the scam curve.”