The holiday shopping season starts in earnest Thursday for many retailers eager to get a jump on competitors and offer consumers more opportunity to spend money.

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The stakes are high: Last year, day-after-Thanksgiving sales rose 6.6 percent to $11.4 billion, according to the Chicago-based research firm ShopperTrak, making it the largest single shopping day of the year. And today and Friday kick off a holiday season that can account for as much as 40 percent of their annual revenue and put them “into the black” for the year — thus the nickname “Black Friday.”

This year, though, several retailers are making it a “Gray Thursday” by opening on the holiday itself — some of them in the evening, others even earlier. Toys R Us, Kmart, Sears, Wal-Mart, Target, Old Navy and Gander Mountain are just a few of the retailers that have backed up their opening times into Thanksgiving, with several large shopping malls and many more retailers opening at the stroke of midnight tonight.

More than half of American consumers plan to do some shopping this weekend, with about one-third hitting the stores on Black Friday alone, according to the International Council of Shopping Centers. Yet for some, the trend of retailers moving toward Thanksgiving Day openings represents a greed-fueled encroachment on the family time.

A handful of online petitions have been launched calling upon retailers to back off their Thanksgiving Day openings to allow employees to spend the entire day with their families, but no retailers have adjusted their previously announced hours as a result of such pressure. And on social media sites such as Facebook, some shoppers have embraced the early sales as a great excuse to get off the couch and enjoy a little family bonding time while searching out bargains.

The CEO of J.C. Penney, which will open at a comparatively late 6 a.m. Friday, took a shot at some of his competitors’ early opening times in an email to customers late Tuesday.

“I know that some retailers are opening on Thanksgiving this year. But spending Thanksgiving with family is one of America’s greatest traditions,” CEO Ron Johnson wrote. “Since jcp was founded on the Golden Rule, I’m proud to honor this tradition by keeping our stores closed on this special day.”

Other retailers say their customers have embraced the earlier opening times. Toys R Us will open at 8 p.m. tonight, an hour earlier than last year, after finding that customer response to last year’s Thanksgiving hours was overwhelmingly positive, according to company spokeswoman Adrienne O’Hara.

“Many people brought their kids and turned it into a family event,” O’Hara said. “And they avoided having to wait in long lines outside during the early morning hours.”

The first 200 people in line at every Toys R Us store will receive a “goodie bag” of stocking stuffers and snacks valued at about $30, O’Hara said. Once inside, they’ll have first crack at 200 “door-buster” specials.

Several of the early-opening retailers are staggering their door-buster specials, offering one set of deals when they first open their doors, and a second and in some cases third wave of specials with later start times Friday morning and afternoon.

For those who are traveling tonight, and those who just make a small dent in their holiday shopping this long weekend, “Cyber Monday” is just around the corner, and several retailers that sell online are starting their promotions over the holiday weekend and extending them through Monday. Shop.org and the National Retail Foundation say that online retailers are poised to unveil some promotions on Monday, with four in 10 retailers offering free shipping without conditions that day.

Shop.org’s eHoliday survey shows that a record 85 percent of retailers with a presence online will offer special promotions on Cyber Monday, up from 78.4 percent last year.

And even those who shop at work may find it easier to do so this year. In a recent survey by staffing firm Robert Half Technology, 33 percent of chief information officers interviewed said their companies block access to online shopping sites, down from 60 percent last year.