The health department of the canton of Graübunden has warned face shield wearers that they offer little protection against the virus.
Plastic visors are also not effective at preventing an infected person from sharing the virus, the doctor warned.
The plastic shields are especially popular in hospitality and beauty services such as hairdressing.
However cantonal doctor Marina Jamnicki said not only are they less effective than face masks, they may provide wearers with a false sense of security.
Plastic face shields should be worn in tandem with a face mask, say cantonal authorities.
According to the cantonal authorities, the situation in the canton has worsened in the past few days.
Swiss media outlet 20 Minutes reports that several people have been infected in the past few days despite wearing face shields.
There are currently 136 people in quarantine in the canton with the virus.