Images from the event showed the singer, who was celebrating the album release edition of her new poetry collection – Violet Bent Backwards Over the Grass – taking part in a reading and then taking pictures with fans.
The event took place at Barnes & Noble at The Grove in Los Angeles on Friday 2 October.
LA county has asked that everyone wear a cloth face covering when interacting with people outside of their households, in both private and public spaces.
California has been one of the worst-hit states in the US during the coronavirus pandemic, with more than 828,000 confirmed cases and over 16,000 deaths.
— Pop Crave (@PopCrave) October 3, 2020
Fans and critics on social media called Del Rey’s use of a mesh mask “irresponsible” and “a danger to herself and others”.
“I love Lana but this is incredibly irresponsible,” one wrote.
“Girl we're in the middle of a pandemic,” one fan wrote on Instagram.
Del Rey’s sister, Caroline “Chuck” Grant, responded to people criticising the singer by claiming she had “tested negative” and was standing “more than six feet away”.
However, images showed Del Rey, 35, standing directly next to fans as she posed for photos.
The Independent has contacted Del Rey’s representatives for comment.
Many responded to a widely shared post from Twitter account @PopCrave, which showed Del Rey posing next to fans.
“This is the most bizarre mask I’ve ever seen and of course Lana Del Rey is wearing it,” someone wrote.