When does your co-worker also count as your supervisor? The Supreme Court may make a final decision on whether to draw a legal line between work colleagues and work managers, at least when it comes to harassment and retaliation claims.

At issue during oral arguments Monday was a decision by the 7th U.S. Circuit Court of Appeals, which declared that only a person with the ability to fire or hire employees can be considered a supervisor, regardless of the person's other duties. But other federal appeals courts — and the Equal Employment Opportunity Commission — have a broader test, saying a person can be a supervisor if they have the authority to direct daily work activities and can undertake or recommend "tangible employment decision affecting employees."

The case was brought to the Supreme Court by Maetta Vance, who was a catering specialist at Ball State University. She accused a co-worker, Shaundra Davis, of racial harassment and retaliation in 2005, and sued the school under the Civil Rights Act of 1964, saying the university was liable since Davis was her supervisor. But a federal judge threw out her lawsuit, saying that since Davis could not fire Vance, she was only a co-worker, and since the university had taken corrective action, it was not liable for Davis' actions. The 7th Circuit upheld that decision, and Vance appealed to the Supreme Court.

Antidiscrimination law prohibits creation of a hostile work environment, and supervisors are held to a higher standard than co-workers since they are in a position of authority over other employees. If the 7th Circuit decision is upheld, advocates say, it will become more difficult for employees to hold employers liable for harassment on the job.

But Justice Elena Kagan, former professor and then dean of Harvard Law School, made clear that she didn't agree with the lower court's definition. "I don't even understand the 7th Circuit's test," Kagan said.

Say, Kagan asked, a secretary for a college professor is being subjected to "living hell" by the professor. Would the secretary, who is hired not by the professor personally but the university's secretarial services, be able to sue the university under the supervisory rules under the 7th Circuit decision? she asked.

"The professor does not apply as a supervisor," answered Sri Srinivasan, a deputy solicitor general.

But Chief Justice John Roberts and Justice Samuel Alito didn't seem a fan of the EEOC's definition of supervisor when it comes to harassment claims, with the chief justice saying that the 7th Circuit decision at least made it clear who can or cannot sue. What if, Roberts said, a senior employee gets to pick the music that employees have to listen to at work and says to a junior employee, "If you don't date me, it's going to be country music all day long."

Or "hard rock," added Justice Antonin Scalia, to chuckles from the courtroom.

The choice of music affects an employee's daily work, Roberts said, as would other privileges given to senior employees. At least with the 7th Circuit's rule, "you don't have to go through case-by-case," Roberts said.

In an unusual move, lawyers for Vance, the federal government and Ball State University all agreed that the 7th Circuit got it wrong, saying the definition of "supervisor" should be broader than what the appeals court had ruled. The 7th Circuit's "rule does not well fit the reality of the workplace," said Daniel R. Ortiz, Vance's lawyer.

"There's broad agreement on what the standard should be," said Gregory G. Garre, lawyer for Ball State University, who argued that even though the definition should be broader, Davis still would not be considered a supervisor.

Their agreement seemed to frustrate some of the justices because they expected to hear an argument over what the lower court did, not an agreement that it was wrong. "There's no one here defending the 7th Circuit," Scalia said at one point.

The justices are expected to make a decision sometime next year.

Several groups have filed amicus briefs because of its possible impact on human resources, including the Chamber of Commerce of the United States, the American Council of Education, the National Partnership for Women & Families, and the Equal Employment Advisory Council.

Indiana University Maurer School of Law associate professor Deborah Widiss said the question of who "counts" as a supervisor for purposes of racial and sexual harassment is extremely important for workers across the country. She said in a statement released by the law school that some courts' definitions of "supervisor" in anti-discrimination law doesn't match the reality of today's workplace.

"The lower courts in Vance held that only individuals who had authority to make formal personnel decisions, such as hiring, promotion or termination, should be considered 'supervisors,'" she said. "However, employees often have minimal contact with the people who make those formal decisions, but they interact every day with intermediate supervisors, such as shift workers. And these intermediate supervisors are often the ones who are best positioned to create a hostile work environment."

Widiss hopes that the justices will broaden the definition of "supervisor" to include employees who control other employees' daily work or who can use their authority to facilitate harassment.