I've seen some vegan business owners talking about how they're going to refuse to accept them as payment. I could be wrong (and someone will no doubt correctly me swiftly and coldly if I am) but I was led to believe that if something is declared legal tender, then as a business you are legally required to accept it as payment?
I remember a while back on another forum there was a big kerfuffle about accepting payment in the form of hundreds of pennies, nickels and dimes. People didn't want to do it because it was inconvenient and frankly a pain in the backside, but because those coins were still legal tender, the payment had to be accepted.
As I understood it (and again, I could be wrong), the only exception is if you're trying to pay for a pack of gum with a benjamin at the buttcrack of godawful in the morning, when they haven't been to the bank and physically can't make that much change - so then it's not so much a case of "I am refusing to take your money" as it is a case of "I literally do not have enough change in the register to process this payment, it's a logistic thing not me being uppity".