Amazon.com CEO Jeff Bezos challenged his rivals to ante up.

In his annual letter to shareholders.

He called on other retailers to match Amazon's MINIMUM wage or even better, beat it.

The billionaire writes, "Today, I challenge our top retail competitors (you know who you are!) to match our employee benefits and our $15 minimum wage.

Do it!

Better yet, go to $16 and throw the gauntlet back at us." The online retailer hiked its minimum wage in the U.S. in November just as retailers and shippers competed to hire workers for the holiday shopping season amid unemployment at a nearly 20 year low.

Bezos said in his letter that the wage hike has benefited more than 250,000 Amazon employees and over 100,000 seasonal workers.

By contrast, Bezos' total compensation last year: $1.7 million.

That's 58 times the median pay at Amazon.