"$5 FEE ADDED TO ORDERS PLACED WHILE WEARING A FACE MASK," reads signs posted in the windows and at the register of Fiddleheads Cafe.
The fine print adds that anyone overheard bragging about having been vaccinated will be hit with another $5 charge.
"Customers either love it or hate it," said owner Chris Castleman in an email to NBC Bay Area, who said the 'fee' is ultimately considered an 'optional donation' which goes to charities assisting victims of domestic abuse.
"There are people who refuse to pay it; I guess a $5 donation to charity is too much for them. Others have gladly paid it knowing that it goes to a good cause. I don't force anyone to pay, I give them the freedom of choice, which seems to be a foreign concept in these parts of the country," Castleman added.