A union organization filed a complaint Friday with the National Labor Relations Board, accusing Apple of anti-union actions. It's the latest in a year of clashes between the company and a small number of its retail employees engaged in collective organizing. 

The Communications Workers of America, or CWA, which has been supporting employees of an Apple store in Columbus, Ohio, filed the complaint to the US labor board. The complaint accuses Apple of trying to get those employees to join an "employer-created / employer-dominated labor organization as a means of stifling union activities" as well as holding mandatory anti-union meetings, according to a Bloomberg report. 

Apple didn't immediately respond to a request for comment. 

In May, the CWA filed a complaint with the NLRB against Apple alleging the tech company had kept workers from distributing pro-union materials in a New York City retail store break room, and in October the labor board itself filed a complaint with Apple stemming from the CWA's filing. Other complaints filed with the labor board allege unfair labor practices by Apple. 

Amid the complaints, workers have had mixed success organizing their stores into official unions. Employees from two stores, in Maryland and Oklahoma City, successfully voted to unionize in June and October, respectively, becoming the first two groups of Apple retail store workers to do so. But a group of workers at an Atlanta store backed out of holding a union vote in May, saying that a "free and fair election" was impossible.