The boss of Twitter and Square has said that both firms will honour Juneteenth as a company holiday in America.
Jack Dorsey also said Twitter was working to identify which days it made most sense to recognise the end of slavery in other countries.
Juneteenth is observed by many African-Americans on 19 June every year to mark the emancipation from slavery in the US.
It comes as companies respond to Black Lives Matter protests around the world.
The roots of Juneteenth, which is also known as Freedom Day and Jubilee Day, date back to 1865, when Union Army General Gordon Granger arrived in Texas to spread news that the American Civil War had ended and slavery along with it.
More than two years earlier President Abraham Lincoln had signed the Emancipation Proclamation to abolish slavery, but the practice continued in parts of the country after the end of the war.
The day is traditionally celebrated by local events which often include readings of the Emancipation Proclamation, traditional songs and the reading of works by noted African-American writers.
Mr Dorsey made the announcement in a series of tweets, saying it would be a “day for celebration, education, and connection”.
Last week Mr Dorsey tweeted that he was making a $3m (£2.4m) donation to former NFL player Colin Kaepernick’s Know Your Rights Camp to “advance the liberation and well-being” of minority communities.
Mr Kaepernick is best known for kneeling during the US national anthem when he was a player for the San Francisco 49ers to protest against police killings of African-Americans.
His protests were heavily criticised by conservative figures including US President Donald Trump.
The announcement comes as other major US companies have voiced their support for the Black Lives Matter protests for racial justice after the death in police custody of African-American man George Floyd.
Also last week, tobacco giant Altria said it would celebrate Juneteenth as a corporate holiday to give employees time for “personal reflection and healing” and said that it would donate $5m to organisations that address racial inequality.
Some technology firms – including Google owner Alphabet, Uber and Intel – have also pledged millions of dollars in donations to organisations working on racial justice.
Several large Silicon Valley companies have faced criticism in recent years for the lack of racial and ethnic diversity in both their staff and leadership.
Meanwhile, Japan’s SoftBank has launched a $100m fund that will invest in companies led by “people of colour”.