Starbucks Corp will close 8,000 company-owned US cafes for the afternoon on May 29 so 175,000 employees can undergo racial tolerance training in response to protests and calls for boycotts after the arrest of two black men waiting in a Philadelphia store.

The company said in the Tuesday announcement that it will also provide training materials for non-company workers at the roughly 6,000 licensed Starbucks cafes that will remain open in locations such as grocery stores and airports.

The announcement from world's biggest coffee company comes as it tries to cool tensions after the Philadelphia incident last week sparked accusations of racial profiling at the chain, which is the subject of a boycott campaign on social media.

The controversy is the biggest public relations test yet for new Starbucks Chief Executive Kevin Johnson, who already was fighting to boost traffic to Starbucks amid competition from coffee sellers ranging from hipster cafes to fast-food chains and convenience stores.

"While this is not limited to Starbucks, we're committed to being a part of the solution," said Johnson, a former technology executive who took the helm about a year ago.

Even if the threatened boycott does not materialize, the 8,000 temporary store closures will almost certainly have an impact on sales. Starbucks did not say how many hours the stores would be shuttered on May 29, but the afternoon is the slowest time for Starbucks' business.

Starbucks is one of the most high-profile and beloved brands in the world and its long-time CEO Howard Schultz was not one to shy away from difficult conversations over thorny issues such as gay marriage, gun control and Congressional gridlock.

However US race relations have proven more challenging, even for a company that touts its diverse workforce -- minorities account for 18 percent of Starbucks executives with the title of senior vice president or higher and 43 percent of employees overall.

For example, the company's 2015 "Race Together" campaign to foster a conversation on the topic following the high-profile police shootings of several unarmed black men stirred an intense social media backlash.

Johnson has apologized for the "reprehensible" arrests of the two men in Philadelphia on Thursday and took personal responsibility for the incident, which was captured in a customer video that was shared widely.

Starbucks attorneys said Johnson and the men, who were released without charges, have "engaged in constructive discussions about this issue as well as what is happening in communities across the country."

The manager, whose call to Philadelphia police led to the men's arrests, is no longer working for Starbucks.

Philadelphia's police commissioner defended the arrests, saying his officers had to act after Starbucks employees told them the pair were trespassing.

"It's good that Starbucks is giving all staff race trainings on May 29. But let's not lose sight of the real problem which is police accountability," Tiffany Dena Loftin, director of the youth and college division at NAACP, told Reuters

Shares in Starbucks closed up 0.7 percent at $59.83 on Tuesday and are relatively unchanged in the week since the arrests.