Supervisors are not protected by the National Labor Relations Act (NLRA), the federal law that codifies workers' rights to organize, join unions, and bargain collectively with employers. Because supervisors are considered to be part of a company's management rather than its labor force, they cannot join unions and do not enjoy the other rights conferred by the NLRA.

The National Labor Relations Board (NLRB) recently issued a decision clarifying which employees are supervisors and which are not. In Oakwood Healthcare Inc., 348 N.L.R.B. 37 (2006), the Board found that employees who have the authority to make work assignments or direct the work of other employees may be supervisors if those tasks require some independent judgment and discretion, even if they spend only 10% to 15% of their time on these supervisory duties. This decision represents a change from previous NLRB decisions, which interpreted the term "supervisor" more narrowly.

Previously, the NLRB found that employees who used ordinary professional or technical judgment in directing less skilled employees to provide services were not exercising independent judgment, and therefore did not qualify as supervisors. But the U.S. Supreme Court rejected this interpretation as too limited (NLRB v. Kentucky River Community Care, Inc., 532 U.S. 706 (2001)). In response to the Supreme Court's ruling, in Oakwood, the NLRB abandoned its earlier interpretation.

In Oakwood, the NLRB focused on two supervisory responsibilities: assigning work and directing the work of other employees. The NLRB found that an employee who assigns others to particular departments, shifts, or significant tasks is a supervisor, as long as making those assignments requires some independent judgment and discretion and is not simply clerical or routine in nature. An employee who responsibly directs others -- that is, who oversees the work of other employees and is held accountable for their performance -- also qualifies as a supervisor.

The Oakwood case involved charge nurses at a hospital, but the decision is expected to have significant repercussions beyond the healthcare field. Many employees who do not make hiring and firing decisions but exercise some authority over other employees will be classified as supervisors by the NLRB -- even if they spend most of their time doing the same work as the employees they supervise. The decision is widely expected to exclude more employees from union membership, although commentators for business and labor groups disagree on how many employees will be affected.