A Wal-Mart Stores Inc. (WMT) worker said he was disciplined for using Facebook to rail against a boss's "tyranny." A crime reporter in Tucson, Arizona, was fired for using Twitter to taunt that the city had too few homicides.

The National Labor Relations Board, which acts on unfair-labor practices, has reviewed 129 such cases since 2009 involving social media and the workplace, most filed this year, according to a study to be released today by the U.S. Chamber of Commerce, the nation's largest business lobbying group.

The five-member labor board and its general counsel have sided with employers in some cases, agreeing workers can be fired for gratuitous "griping" about the boss. In other circumstances, the government has contended employees were exercising a right to speak out about workplace conditions. The NLRB risks creating a right to Twitter-bomb the boss with online insults, said Michael Eastman, who prepared the study for the Washington-based Chamber.