The group of pharmacists and pharmacy technicians won an initial ballot 7-2 in favor of forming the union, the filing showed.

The National Labor Relations Board in 2011 ruled that so-called micro unions are appropriate when their members share "a community of interest."

That decision was upheld by a U.S. appeals court, spurring the board in 2014 to extend the standard to retail stores in a case involving fragrance and cosmetic department workers at Macy's Inc.

Target did not immediately respond to requests seeking comment.

(Reporting by Nandita Bose in Chicago, Additional reporting by Dan Weissner, Editing by David Greising)