The retail giant has filed a complaint with a federal agency.
Walmart accuses the United Food and Commercial Workers Union of unlawfully organizing picket lines.
Meantime, Wal-mart workers at 1,000 locations say they are angry that the company plans to open stores at 8:00 p.m. on Thanksgiving night.
Cities including Chicago, Dallas, Miami, Milwaukee and Los Angeles could see walkouts by Walmart employees as early as Monday.
