NEW YORK -- Walmart (WMT.N) is expanding its grocery delivery service with ride-hailing service Uber to two more markets -- Dallas and Orlando, Florida.

The world's largest retailer had launched a pilot grocery service with Uber Technologies Inc. last year in Phoenix and then Tampa, Florida, earlier this year. The delivery charge is US$9.95

The move, announced Monday, marks the latest steps that Walmart is taking to offer more options for online grocery shoppers amid increasing competition from online leader Amazon.com. The stakes are getting higher with Amazon's announcement in June to buy Whole Foods Market. On Wednesday, stockholders of Whole Foods are expected to approve Amazon's US$13.7 billion takeover bid.

The Bentonville, Arkansas-based discounter operates its own grocery delivery system in San Jose, California, and Denver. It also has curbside grocery pick up service for online shoppers at more than 900 of its stores.

"We're working hard to find a way to get you fresh, quality groceries all while keeping a little more time on your calendar," wrote Mike Turner, vice-president of Walmart's e-commerce operations, in a corporate blog post.