(Reuters) – Amazon.com Inc Chief Executive Officer Jeff Bezos on Thursday challenged rival retailers to increase their minimum wages to $16 an hour.

“Today I challenge our top retail competitors (you know who you are!) to match our employee benefits and our $15 minimum wage,” the billionaire entrepreneur said in a letter here to shareholders.

“Do it! Better yet, go to $16 and throw the gauntlet back at us.”

The online retailer giant raised its minimum wage to $15 per hour for U.S. employees from November, giving in to critics of poor pay and working conditions at the company.

Amazon’s wage hike came at a time when U.S. unemployment was at a near two-decade low as retailers and shippers were competing for hundreds of thousands of workers for the all-important holiday shopping season.

Bezos said in his letter that the wage hike has benefited more than 250,000 Amazon employees and over 100,000 seasonal employees who worked during the last holiday season at Amazon sites in the United States.

Amazon’s third party sales in 2018 accounted for 58 percent of total sales, up from 56 percent in 2017, Bezos said.