"The Subcommittee is concerned that FDA is not conducting substantive review of serological tests that it has allowed on the market and that those tests may not meet a reasonable standard of accuracy," Krishnamoorthi said in the letters, which were sent to North Carolina-based BioMedomics, San Diego's Epitope Diagnostics, Minnesota-based Premier Biotech and San Jose's UCP Biosciences.

The FDA waived its typical quality checks to help antibody tests reach the market quickly, instead allowing companies to self-evaluate the accuracy of their products. Researchers have begun issuing evidence that many of the tests are falling short of typical accuracy standards, producing false positives that could lead people to believe they've developed protection against the virus.

Krishnamoorthi pointed to evidence obtained by University of California researchers that tests marketed by the companies he's targeting fall short of the accuracy they claim in their marketing materials and instructions for use. In addition, UCP Biosciences has not been identified by the FDA as one of the 150 tests allowed on the market, yet its tests were purchased by a 25-bed hospital in rural Kansas, according to local reports.

An earlier staff report by the panel raised alarms about the lack of controls on the market for antibody tests, warning of "fraudulent" products and scolding the FDA for issuing "unclear guidance" while failing to police the market for these tests. And in a new letter to FDA Commissioner Stephen Hahn, Krishnamoorthi demands by May 6 information about the FDA's process for retroactively reviewing antibody tests that have come to market, whether any have met the agency's standards for approval and whether any have been removed or faced enforcement actions because they fell short.