Starbucks is celebrating its annual Red Cup Day today, offering customers a free limited edition 16-ounce reusable red cup with the purchase of select holiday beverages.

Supplies are limited, and the giveaway could be disrupted by labor actions.

Union members at Starbucks voted to approve a nationwide strike on Red Cup Day unless a contract agreement was reached.

Workers in at least 25 cities are planning to strike, though it's unclear how many locations will be affected.