The CDC on Friday for the first time recommended that people wear masks at all times when they’re not home, saying the coronavirus pandemic in the U.S. has entered a phase of “high level transmission.”

The guidance, included in a new report, advised state and local officials to impose mask mandates for indoor settings as part of broader mitigation efforts to control the spread of the virus. It echoes President-elect Joe Biden’s call for mask orders that a number of red state governors have rejected.

The context: This is the first time the CDC has recommended universal mask-wearing, including indoors. The agency for months has endorsed face coverings, and in July released a study touting their effectiveness in community settings to reduce transmission of the virus.