Mission Viejo, Calif.-based Vivera Pharmaceuticals has received an FDA warning letter for marketing unapproved tests for the coronavirus that causes COVID-19.

The agency says it visited the company’s websites and found they offered a COVx-RDA Saliva Antigen Test and a COVx-RDA Nasal Antigen Test that were not authorized.

Vivera’s COVID-19 test kits are considered adulterated and misbranded, the agency said, adding that it is taking urgent measures to stop the sale of such products during the pandemic.