WASHINGTON — Longstanding tensions between organized labor groups and Wal-Mart Stores ratcheted up last week at the kickoff to the holiday shopping season.

As SN went to press last week, Wal-Mart was seeking federal intervention to prevent employee groups from disrupting “Black Friday” sales at its stores, as a result of pickets and strikes threatened by union-backed groups of its own workers. The posture represented an abrupt change for Wal-Mart, which earlier this year publicly dismissed similar protests as “publicity stunts.” Moreover, sources said, it provided a peek into the mindset of the retailer and the labor union determined to organize its workers at the dawn of a second term for president Obama.

In an unusual move for the Bentonville, Ark.-based company, Wal-Mart filed an unfair labor practice charge with the National Labor Relations Board, saying that worker walkouts and demonstrations by the group OURWalmart over recent months amounted to union picketing in excess of the 30-day limit federal law without a petition to join a union. This type of charge requires “priority” handling by the NLRB, which last week was scurrying to come to a ruling before courts closed for the Thanksgiving holiday.

The NLRB complaint by Wal-Mart was its first in a decade, the New York Times reported.

While it was unclear early last week what if anything would come of Wal-Mart’s charge, the filing appeared to be an attempt by Wal-Mart to set the boundaries for a battleground where its opponent is energized by having mobilized a small portion of Wal-Mart’s own forces against it, according to Don Schroeder, a Boston attorney who specializes in specializes in employment policy and collective bargaining for Mintz Levin.

“I think principally, Wal-Mart is driving a stake in the ground in an attempt to get the NLRB thinking about putting some limitations upon the unions that have engaged in this ongoing campaign against Wal-Mart,” Schroeder told SN.

Wal-Mart argues that the United Food and Commercial Workers union is behind efforts from employees groups including OURWalmart and Making Change at Wal-Mart, which have called attention to what they consider to be unjust conditions for Wal-Mart workers by staging walkouts beginning in October. Making Change, a coalition led by the UFCW, said there were plans for action at as many as 1,000 Wal-Mart stores leading up to and on Black Friday.