Amazon is giving another pay boost to its subcontracted delivery drivers in the U.S. amid growing union pressure. Drivers who work with Amazon’s Delivery Service Partners, or DSPs, will earn an average of nearly $22 per hour, a 7% bump from the previous average of $20.50, the company said Thursday. The increase in wages is part of a new $2.1 billion investment the Seattle-based online retailer is making in the delivery program.