Tech industry leaders including the Salesforce chief executive, Marc Benioff, and the Apple CEO, Tim Cook, have called on South Carolina to remove the Confederate flag from the grounds of its state house in Columbia.

The calls came after a gunman shot dead nine people at the Emanuel African Methodist Episcopal church in Charleston last Wednesday, apparently because they were black.

The calls from the business community were prompted by an unlikely source – the former Republican presidential candidate Mitt Romney.

“Take down the Confederate flag at the South Carolina Capitol. To many, it is a symbol of racial hatred. Remove it now to honor Charleston victims,” Romney tweeted on Saturday. The same day, President Barack Obama and Benioff came out in support of Romney’s call for removal of the flag.

Hours after Romney’s tweet, hundreds of people gathered at the South Carolina state house to demand that the flag be removed.

“I see the KKK, I see burning crosses, I see burning churches, I see raping, lynching, I see all of that,” Stephanie Bradley, a black woman and mother of three young children, told the Guardian.

Bradley said the flag was a reminder of racism inflicted on black people throughout the course of US history.

On Sunday afternoon, Cook weighed in, tweeting: “My thoughts are with the victims’ families in South Carolina. Let us honor their lives by eradicating racism & removing the symbols and words that feed it.”

Earlier this year, when delivering a commencement address at George Washington University, Tim Cook spoke about growing up in southern Alabama.

“Keep in mind that when I grew up, I grew up in the place where [Dr Martin Luther] King and [Robert F] Kennedy were not held in high esteem,” he said. “When I was a kid, the south was still coming to grips with its history. My textbooks even said that the civil war was about states’ rights. They barely mentioned slavery.”

He went on to say “injustices like segregation have no place in our world” and “equality is a right”.

“Sidelines are not where you want to live your life,” he told the GW students. “The world needs you in the arena. There are problems that need to be solved. Injustices that need to be ended. People that are still being persecuted.”

Cook and Bennioff have previously used their positions to speak out against anti-LGBT bills that had passed in as many as 20 states.

South Carolina’s largest employers include BMW Manufacturing, Piggly Wiggly, Adidas, Kraft, Michelin and Nestlé. These companies did not respond to Guardian requests for comment on the issue of the Confederate flag.