As Wal-Mart workers prepare to stage a walkout on Black Friday, the world's largest store is fighting back.

Wal-Mart (WMT) has filed a complaint with a federal agency accusing one of the largest labor unions in the country of unlawfully organizing picket lines, in-store "flash mobs" and other demonstrations in the past six months.

In its complaint Thursday, Wal-Mart said the United Food and Commercial Workers Union and its subsidiary known as OURWalmart is trying to force the store into collective bargaining even though it is not the official union for Wal-Mart's employees. The UFCW represents over a million meat packers and food industry workers.

The complaint comes just days before Wal-Mart workers' plan to stage nationwide walkouts on Black Friday, arguably the biggest holiday shopping day for any U.S. store. Union-backed groups OUR Walmart and Making Change at Wal-Mart, along with a watchdog group Corporate Action Network are calling on the country's largest employer to end what they call retaliation against employees who speak out for better pay, fair schedules and affordable health care.

The planned walkouts build on an October strike that started at a Wal-Mart in Los Angeles and spread to stores in 12 other cities. More than 100 workers joined in the October actions.

Related: Wal-Mart workers plan Black Friday walkout

Wal-Mart spokesman David Tovar pointed out in a statement that the number of workers participating in the walkout is a "very small minority" of its 1.3 million workforce. Tovar said that Black Friday is like the "Superbowl" for retailers and that Wal-Mart is ready.

"If [the store employees] are scheduled to work, we expect them to show up and do their job. If they don't, depending on the circumstances, there could be consequences," said Tovar.

In a letter to UFCW's general council sent on Friday, Wal-Mart said the workers' ongoing actions violate the National Labor Relations Act, which prohibits picketing for any period over 30 days without filing a representation petition. The retailer said the actions have disrupted business.

"The UFCW has orchestrated numerous pickets, mass demonstrations, flash mobs and other confrontational activities both inside and outside Wal-Mart facilities in support of its bargaining and recognition demands," wrote Wal-Mart lawyer Steven Wheeless. "Now, with the busiest shopping season of the year just days away, the UFCW is openly orchestrating and promoting attempted mass disruptions of Wal-Mart's customer shopping experience."

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OURWalmart organizers say they have 1,000 events planned this week. Support for the campaign, which has been gaining momentum across social media platforms, is mounting: The organization's Facebook page now has more than 28,000 'likes' and its accompanying YouTube video has been watched over 103,000 times.

The organizers have also collected more than $36,000 in online donations to sponsor workers who walk out.

"We remain focused like a laser about trying to build a bigger coalition and support workers as they build their organizations to challenge Wal-Mart stores," said OURWalmart's president Dan Schlademan.

Wal-Mart said that while it respects its workers federally-protected right to express concerns, it will also act to protect its stores and customers "from illegal and unprotected conduct that threatens safety or business operations," such as protesters trespassing on Wal-Mart grounds and interfering with business.

Wal-Mart is rolling out Black Friday deals starting at 8 p.m. on Thanksgiving this year, two hours earlier than it did last year.

Shares of the company were down nearly 6% last week.