The delay deals a blow to Wal-Mart's attempt to stop workers and their supporters from staging major protests at Walmart discount stores on "Black Friday," the day after Thanksgiving that is traditionally the busiest shopping day of the year.

Separately on Tuesday, OUR Walmart, the organization that has been staging the protests, filed its own charge with the NLRB, saying Wal-Mart was illegally attempting to deter workers from participating in strikes against the world's largest retailer on Friday.

Last week, Wal-Mart, which has faced months of protests and rallies outside its stores, filed an unfair labor practice complaint last week against the United Food and Commercial Workers International Union (UFCW), asking the NLRB to halt what the retailer says are unlawful attempts to disrupt its business. Wal-Mart argued the job actions are backed by the UFCW.

In a statement on Tuesday, the NLRB said it was continuing to investigate Wal-Mart's complaint.

"The legal issues - including questions about what constitutes picketing and whether the activity was aimed at gaining recognition for the union - are complex," it said.

The field office considering the case expects to complete its investigation on Wednesday and send its findings to the NLRB Division of Advice in Washington for further analysis.

"Under these circumstances, the Office of General Counsel does not expect to make a decision before Thursday on whether or not to seek an injunction to stop the activity," the statement said.

It was not clear whether the NLRB would be able to get a hearing before the Appellate Court on Thanksgiving, a federal holiday, if it sought an injunction. Most Wal-Mart stores will be open all night on Thanksgiving into Black Friday.

"We understand that the multi-state, multi-faceted nature of the union's conduct and the Board's desire to perform a thorough review of the facts means that a decision will take a bit more time," Wal-Mart spokesman Fogleman said.

According to a filing with the Labor Department, OUR Walmart - a coalition of current and former Wal-Mart staff seeking better wages, benefits and working conditions - was a subsidiary of the UFCW as of 2011.

The UFCW helped OUR Walmart get started with financial and technical assistance, which is reflected in the 2011 filings, but the language in the 2012 filing will not be the same, UFCW spokeswoman Jill Cashen said.

In its own complaint filed on Tuesday, OUR Walmart said the retailer has told store-level management to threaten workers with termination, discipline and/or a lawsuit if they strike or engage in other job actions on Black Friday.

Wal-Mart Chief Financial Officer Charles Holley last week called Black Friday "the Super Bowl" for retail.

"We respect all of our associates and respect their right to share their concerns," company spokesman Fogleman said.

"We are always willing to hear those concerns. There has not been any retaliation against our workers who are simply expressing their views, nor will there be."

(Reporting By Brad Dorfman in Chicago and Ros Krasny in Washington D.C. Editing by Andre Grenon and Ryan Woo)

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