Hamilton star Giles Terera claims a bar refused entry to a group of actors because they were black.
He accuses Aint Nothin But... blues bar in central London of "racial profiling" and says a group of white customers were allowed in past them.
The bar has denied the claims and say some of the actors didn't have ID "so could not be served".
"We have regular customers, and staff, who are black. It makes no difference to us what colour people are," it says.
In a post on Twitter, Giles told his followers he's directing the group of actors in a play about American blues musicians and took them to the bar on Friday.
"We were racially profiled and refused entry as 10 white punters were allowed in past us unchecked," he wrote on Twitter.
1. I just took a group of 8 Black actors who i’m directing in a play about American blues musicians to Aint Nothin But The Blues bar in soho. We were racially profiled and refused entry as 10 white punters were allowed in past us unchecked. WTF @AintNothinBut1 @standardnews RT pic.twitter.com/Ll150lCMi0— Giles Terera (@GilesTerera) November 29, 2019
The actor says the group were left "devastated, confused and upset" and the fact this happened in a venue which "exploits blues music is sick".
In a post on Facebook, the bar - which is in Soho - accused the actors of trying to "use the race card" to intimidate staff.
It says the tweets are "unfair" and "no-one was refused entry".
The bar says the actors were asked for ID and it was "found some of the group did not have ID" and so they couldn't be served.
On its website, it says its age policy is "over 18 years old at all times".
"Just because the next group happened to be white, they were a different age group, so were served," it added.
"We now have an unfair reputation which we cannot properly respond to.
"We have regular customers, and staff, who are black. It makes no difference to us what colour people are."
Giles has received lots of support from other actors since his tweet was posted.
Nathalie Emmanuel, who played Missandei in Game of Thrones, posted: "Ugh this is so infuriating and unacceptable."
Everybody's Talking About Jamie star Layton Williams wrote: "Absolutely gross!! So sorry you had to experience this. Unfortunately I know exactly how it feels.
"Sending cyber love to you all."
Ugh this is so infuriating and unacceptable 😡— Nathalie Emmanuel (@missnemmanuel) November 30, 2019
Absolutely gross!! So sorry you had to experience this. Unfortunately I know exactly how it feels. Sending cyber love to you all 💙— Layton Williams (@LaytonWilliams) November 30, 2019
But customers of the bar have defended it on Facebook, with one saying it is the "friendliest and most welcoming bar in London".
Another said the bar "welcomes people of all nationalities and ethnicities, adding: "In fact it's a great place to meet a huge variety of people who all share a common love for the blues and live music."
Radio 1 Newsbeat has contacted Giles and the bar for further comment.
Aint Nothin But... said it didn't want to make the issue "any bigger" and would be getting legal advice.