As Facebook and Twitter become...central to workplace conversation...federal regulators are ordering employers to scale back policies that limit what workers can say online...Don’t discuss company matters publicly, a typical social media policy will say, and don’t disparage managers, co-workers or the company itself...But in a series of recent rulings and advisories, labor regulators have declared many such blanket restrictions illegal. The National Labor Relations Board says workers have a right to discuss work conditions freely and without fear of retribution...[including] on Facebook. In addition to ordering the reinstatement of...workers...the agency has pushed companies nationwide, including...General Motors, Target and Costco, to rewrite their social media rules...The board’s moves have upset some companies...it is taking a law enacted in the industrial era, principally to protect workers’ right to unionize, and applying it to...nearly all private-sector workers, union and nonunion alike. [also refers to Wal-Mart]