The National Labor Relations Board (NLRB), in a decision unveiled yesterday, ruled on a case that tried to determine which workers -- in this case, nurses -- should be classified as supervisors and prohibited from joining unions. Reaction to the decision has included charges that the NLRB ruling will further weaken organized labor. Ellen J. Dannin, Wayne State law professor and former NLRB attorney, suggests that the National Labor Relations Act, which gives workers the right to organize, is remarkably pro-labor.