The rivalry between Amazon (AMZN) and Walmart (WMT) has heated up once again as Walmart announced that it also will be offering one-day delivery to its online customers. Amazon made its one-day delivery announcement earlier in the month, which may have caused Walmart to respond with a dueling shipping timeframe.

While Walmart’s one-day shipping will start being offered in Las Vegas, Phoenix, and Southern California with full rollout slated for year-end to 75 percent of households, Amazon’s one-day delivery service announcement was not provided with a timeline for commencement.

Amazon did say that it is investing $800 million to make one-day delivery happen for its Prime members, even starting a $1.5 billion development at an airport hub in Cincinnati.

Also, separating the two retailers one-day shipping option is Walmart’s one-day service comes with a $35 minimum purchase while Amazon’s one-day service is free for Prime members.

In the announcement from Walmart, the retailer pointed out that it doesn’t require a membership to receive one-day delivery, which may have been a jab at the cost of Amazon’s Prime memberships. Amazon, however, did not take the news of Walmart’s NextDay delivery service lying down as the e-commerce giant responded on Twitter with a tweet that took a shot at the low-price retailer.

In the tweet, Amazon said, “Others are trying to up their fast shipping game. Fact is, Amazon customers in thousands of cities across 44 major metropolitan areas already have access to millions of items with free SAME DAY delivery. Customers are smart – they know the difference."

Shares of Amazon stock were up 1.68 percent as of 1:54 p.m. EST on Thursday while shares of Walmart stock were up 2.18 percent at the same time.

A staff member collects orders at the Amazon fulfillment center in Peterborough, central England November 28, 2013. The center prepared for Cyber Monday, which is considered the busiest day for online shopping in Britain and will fall on Monday, Dec. 2. Reuters