More than 300 Starbucks stores have held union elections in less than a year, a remarkable feat. But now workers blame "scorched-earth" union busting by Starbucks for a slowdown in the momentum.

Baristas at Starbucks as well as independently owned coffeehouses have driven a surge in union organizing. They see their activism as benefiting not just themselves, but working people broadly.

Once seen as among the most generous of employers, Starbucks is now grappling with disillusionment among its workers. Since December, 20 stores have unionized with more filing for elections every day.

Howard Schultz rejoins Starbucks as interim CEO as the company faces multiple challenges, including an unprecedented wave of unionization at stores across the country.