Starbucks Korea will simultaneously close all its stores for a mandatory history lesson, after a disastrous promotion that evoked memories of a pro-democracy massacre sparked public and political backlash.

More than 2,000 stores will temporarily close at 3pm on 22 June, the company said, so staff can watch recorded lectures on modern Korean history and engage in “social sensitivity” training. The half-day closures will cost Starbucks an estimated 2.1bn won ($1.4m) in lost sales, according to data firm IGAWorks.

The measures follow a public relations crisis triggered when Starbucks Korea ran a discount promotion for its “Tank” tumbler series on 18 May, the anniversary of a 1980 massacre in Gwangju. The promotion led to store boycotts, customers smashing Starbucks mugs and tumblers and government ministries cutting ties with the chain.

Chung Yong-jin, the billionaire chair of Shinsegae Group, which operates Starbucks Korea under licence from its US parent company, will take the same training on 24 June alongside other executives.

Perhaps most surprising here is that the entire thing was homegrown, not an idea someone had in Seattle and forced upon Korea.