The Supreme Court on Tuesday heard highly anticipated cases on whether federal civil rights law should apply to LGBT people, with Chief Justice John Roberts questioning how doing so would affect employers.

In the first of two cases, the justices heard arguments on whether a federal law banning job discrimination on the basis of sex should also protect sexual orientation. Lower courts have split on the issue. A related case on transgender employees is also being heard Tuesday.

Roberts, a possible swing vote in the cases, wondered about the implications of what he described as an expansion of the job-discrimination law.

“If we’re going to be expanding the definition of what ‘sex’ covers, what do we do about that issue?” Roberts asked.

Justice Samuel Alito, a conservative, suggested that the high court would be usurping the role of Congress by reading protection for sexual orientation into the 1964 Civil Rights Act, when lawmakers at the time likely envisioned they were doing no such thing.

“You’re trying to change the meaning of ‘sex,’” he said.

Justice Elena Kagan, a liberal, suggested sexual orientation is a clear subset of sex discrimination, saying that a man who loves other men cannot be treated differently by an employer than a woman who loves men.

The cases Tuesday are the court’s first on LGBT rights since Justice Anthony Kennedy’s retirement and replacement by Justice Brett Kavanaugh. Kennedy was a voice for gay rights and the author of the landmark ruling in 2015 that made same-sex marriage legal throughout the United States. Kavanaugh generally is regarded as more conservative.