Walmart holiday shopping specials are displayed on a computer screen in New York.

In its ongoing struggle to lure Web shoppers from Amazon.com, Wal-Mart has picked up a new ally: messaging start-up Tango.

As of Tuesday, consumers in the U.S. can shop for 2 million products—everything from apparel and jewelry to electronics—via Tango. A shopping tab will appear on the service allowing users to purchase products from Wal-Mart and Chinese e-commerce giant Alibaba.