The decision, which may make it easier for companies to classify millions more workers as management and therefore be ineligible for collective bargaining, angered union representatives. They're likely to appeal in a circuit court.

A permanent resolution may depend on Congress changing the legislation that has governed unionization since 1947. That legislation defines a supervisor as anyone who has the authority to "hire, transfer, assign ... or responsibly to direct" other employees.

It's the assigning and directing that were at the heart of the NLRB decision. The panel held that permanent charge nurses at Oakwood Heritage Hospital in Michigan should be designated as supervisors because they assigned patients to other nurses, influenced their work hours, were responsible for their performance and exercised independent judgment.

In two related cases, however, the board found that nurses at Golden Crest Healthcare Center in Minnesota and lead workers at Croft Metals Inc. in Mississippi did not meet the Oakwood test.

Unions asserted that under the NLRB parameter, a nurse who spends as little as 15 percent to 20 percent of his or her time in the charge role could be considered a supervisor.

Congress may have to sort it out. "Serious consideration ought to be given to amending the statute," says Sarah Fox, a lawyer and former NLRB member.

The NLRB used the three cases to respond to a 2001 U.S. Supreme Court ruling in NLRB v. Kentucky River Community Care Inc. In that action, the high court rejected the board's reasoning when it upheld a union request to include six registered nurses in a bargaining unit.

"Employers should be satisfied because they have more clarity in what (responsibility) to give to individuals if they wish them to be a supervisor," says James Redeker, chair of employment services at WolfBlock, a Philadelphia law firm. AFL-CIO president John Sweeney said in a statement that the NLRB decision was the latest step by the Bush administration "to deny as many workers as possible their basic right to have a voice on the job and improve their living standards through their union."

The three Republican appointees to the board voted in favor of the supervisor definition. The two members backed by Democrats dissented, writing that the decision threatened to create a class of workers who "have neither the genuine prerogatives of management, nor the statutory rights of ordinary employees." Peter Kirsanow, who was appointed to the NLRB by President Bush in January, maintains that the board is not overtly political.

"There's an effort to incorporate the views of everyone before you come to a conclusion on a particular case," he said in an April interview.

The NLRB ruling could have a wide impact. Computer scientists, engineers and other skilled employees could be defined as supervisors in today's collaborative offices.

"It's all about pushing authority down to frontline workers," Fox says.

—Mark Schoeff Jr.