(Cyber Monday article updated with Home Depot free-shipping offer.)

NEW YORK (

TheStreet

) -- Door-buster deals are no longer enough to woo customers this holiday season. Free shipping has become a must for retailers, potentially making or breaking online sales this Christmas.

According to Shop.org, four out of five online retailers will offer free shipping at some point during the holiday season, with about one-third saying these deals started earlier than last year.

Indeed, shoppers are being trained to wait for free shipping to kick in and to look elsewhere if an Internet retailer doesn't offer a promotion. According to comScore, 50% of consumers said they would abandon their online shopping cart if free shipping is not offered.

This is especially relevant as the holiday sales continue to gain presence online, with shoppers utilizing both online coupons and social networks like Facebook to offset some weakness at brick-and-mortar stores.

Still, while Black Friday continues to surpass Cyber Monday in terms of sales volume, Dec. 17, known as Green Tuesday, or free-shipping day, is gaining momentum.

On Dec. 17, more than 1,000 online merchants will offer some sort of free shipping deal.

But retailers are not waiting until Dec. 17, and most aren't even holding off until Black Friday, to start rolling out free-shipping offers.

Wal-Mart upped the ante early in the season, announcing that it will offer free shipping on 60,000 items -- including electronics, jewelry and toys -- through Dec. 30. The best part: there is no minimum purchase requirement, which is more than can be said for some of its rivals.

In response to this offer,

Amazon

(AMZN) - Get Report

, which is typically the leader in shipping, promised to match or beat any free shipping offer from competitors, as well as provide 30-day free returns.

Normally, Amazon offers free shipping to its Amazon Prime members, who pay $79 a year for membership.

Best Buy

(BBY) - Get Report

also does not require a minimum order for its free shipping promotion, which features hundreds of thousands of items, including CDs, DVDs, video games and video game accessories. But the promotion, which runs until Dec. 21, does exclude popular gifts like

Apple's

(AAPL) - Get Report

iPad, video game consoles and major appliances.

Home Depot

(HD) - Get Report

announced it will provide free shipping on more than 90,000 products, including holiday decor, power tools and appliances, also with no minimum purchase. This promotion will run from Thanksgiving Day until Cyber Monday.

Barnes & Noble

(BKS) - Get Report

will offer free shipping on Cyber Monday.

But there are other retailers whose free-shipping deal comes with a catch.

Target

(TGT) - Get Report

,

Toys 'R' Us

and

Gap's

(GPS) - Get Report

Old Navy require a $50 minimum purchase in order to receive free shipping

Target's deal will also end sooner than most other retailers, expiring on Dec. 11.

Macy's

(M) - Get Report

will offer free shipping for the first time this season, but shoppers must first spend $99 on its Web site. The deal will end of Dec. 20.

Rival

J.C. Penney

(JCP) - Get Report

said that online orders of $25 or more are eligible for free shipping from Nov. 24 through Nov. 30.

-- Written by Jeanine Poggi in New York.

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