Jack Dorsey, the boss of the micro-blogging platform and Square, has confirmed that both firms will honour Juneteenth as a company holiday in the US.
He wrote on Twitter: "Both Twitter and Square are making #Juneteenth (June 19th) a company holiday in the US, forevermore. A day for celebration, education, and connection.http://www.juneteenth.com/history.htm (sic)"
Juneteenth is observed on June 19, and is a date that's used by some Americans to mark the emancipation from slavery in the US.
Twitter is also seeking to find specific days to mark the end of slavery in other countries.
In May, meanwhile, Twitter announced its employees can work from home forever.
The micro-blogging site decided to give its staff the option to continue their work from home, where possible, because during the coronavirus pandemic it has been possible to continue working.
In a statement, the firm said: "The past few months have proven we can make that work.
"So if our employees are in a role and situation that enables them to work from home and they want to continue to do so forever, we will make that happen."