One said the comments they've received from punters have been so hostile they've even considered closing their business altogether.
The introduction of the Covid pass is the result of Welsh Government having passed restrictive legislation by one vote on certain types of music events at certain times during a controversial Senedd meeting last week.
It requires members of the public to provide evidence of their vaccination status. That includes proof of a double jab or of a negative lateral flow test taken up to 48 hours prior to visiting a venue.
Without these entry will not be permitted and any business choosing to defy the law faces being fined and closed down.
Suzanne Reynolds, who runs Slipping Jimmy's Bar & Grill, said she's even considered closing the business over the amount of flak she's received.
"We're been called Nazis, morons, everything you can think of," said the 49-year -old who, along with her husband Steve, set up shop on the city's High Street back in 2015.
"We've had regulars - people we've come to know and previously got along with - turn really nasty and accuse me of persecuting them.
"I've had some tell me, 'I hope you get what's coming to you'. It's like they don't understand that this isn't our decision. It's not personal, it's the law.
"Honestly, I've been in bits over it and it's made me wonder if all the hassle is worth it.
"Me and Steve have put our hearts and souls into this place, but I genuinely dread opening now - especially with this weekend being the first proper weekend since this law was passed.
"I just hope things don't kick off - I've even had to hire extra door staff in case it does."
Music Venue Trust, a registered charity representing the interests of grassroots venues across the UK, stressed that punters need to channel their frustration in the right way.
"If you are annoyed by these laws, you should write to your MP or MS," said a spokesperson.
"Or you can demonstrate on the streets - whether you're in favour of them or against them.
"But what you should not be doing is posting bile and stupidity on the social media pages of your local venue, or sending them hate mail, calling them Nazis or leaving threats on their booking lines.
"All of which a cabal of idiots have decided to do in the last few days. So if you see behaviour like this, please support your local venue by clamping down on it."