A UPS worker carries an Amazon box to be delivered in New York in July. Eduardo Munoz | Reuters

Amazon Prime Day isn't just about the deals on Amazon anymore. In its fourth year, the annual shopping event is now drawing the attention of rivals eBay, Target, Kohl's, Macy's and more. It's great news for shoppers looking to save money next week but added pressure for those companies already losing market share to the e-commerce behemoth. Coresight Research is estimating Prime Day 2018 sales should reach at minimum $3.4 billion globally, breaking another record. If that threshold is achieved, it will make July 17 the biggest shopping day ever for Amazon in terms of revenues, ahead of Cyber Monday 2017, said Coresight CEO and Founder Deborah Weinswig. The fact that other retailers are starting to plan their own promotional events around Prime Day shows just how important the event has become for the industry. Amazon last year said a record "tens of millions of Prime members" rang up purchases during Prime Day. With so much traffic online, other companies can't afford to miss an opportunity to win some of those sales, especially as Amazon becomes a bigger and bigger threat. PwC consumer markets lead Steve Barr said, "July has turned into a mini holiday shopping season" with all the activity piling on. It could one day surpass the shopping done around Black Friday or Cyber Monday.

In the U.S. alone, 76 percent of online shoppers are "very likely" or "somewhat likely" to visit Amazon during Prime Day this year. That's according to a March survey of roughly 1,000 respondents ages 18 and older, which was run by Digital Commerce 360. Phillip Dengler, co-owner of the website BestBlackFriday.com, said his team is expecting at least 70 percent of comparable Prime Day prices to be better than those of Black Friday 2017. Prime Day kicks off at 3 p.m. ET on Monday, and runs 36 hours through Tuesday. Shoppers must be a Prime member to snag any of the deals. Memberships now cost $119 per year.

Where the deals are

Target said Friday it will have a day of deals next Tuesday as well. It emphasized there's "no membership required" to be eligible for discounts on home furnishings, cookware, toys and Google products, for example. Target will also be giving shoppers who spend more than $100 on Target.com on July 17 a free six-month membership for same-day delivery via Shipt. A membership to the delivery service typically costs $99 for the year. Ebay, one of Amazon's biggest rivals online, said it will offer "thousands of exclusive deals" on Tuesday. Like Target, eBay is touting "no membership required ... ever." Ebay also just last month updated its price-matching policy to offer U.S. shoppers 110 percent of the price difference if they're able to find an item for less on an approved competitor's website — that list includes Amazon, Best Buy, Sears, Home Depot, Target, Walmart and Jet.com. In the department store space, Kohl's and Macy's have their own strategies to compete with Prime Day. Kohl's held a one-day sale event, called "It's A Big Deal," this past Tuesday. One week ahead of Amazon's shopping extravaganza, Kohl's offered discounts on KitchenAid appliances, mattresses, workout clothes and more. Macy's is also trying to draw shoppers in ahead of Prime Day, holding "Black Friday in July" deals all week through this Sunday. Retailers could completely miss a huge wave of online shopping activity ahead of the back-to-school shopping season if they don't chime in. Walmart has a running summer sale but earlier this week kicked off its back-to-school and back-to-college deals. The company has added new experiences to its app, where parents can shop a child's school list specifically and then locate certain items in a store. Walmart, like Target, has also been offering discounts on Google Home products, which rival Amazon's tech gadgets.

WATCH: Amazon is rolling out big deals for Prime Day. Here's what to expect