Employment attorneys are advising companies to rewrite their employee handbooks in response to a National Labor Relations Board ruling this month that will invalidate some existing workplace rules.

“This ruling, in a word, is huge,” David Pryzbylski, an attorney with Barnes & Thornburg in Indianapolis, told the Society for Human Resource Management for a recent article. ”This decision may invalidate countless workplace rules maintained by private-sector employers—whether they are unionized or not. It applies to all companies covered by the National Labor Relations Act, which is the vast majority of employers in America.”