“OK, Boomer,” was uttered for the first time in a Supreme Court session Wednesday as Chief Justice John Roberts, who will turn 65 this month, referenced the phrase used by younger people to dismiss their elders during a case about age discrimination in the workplace.

As the leader of the Supreme Court, Roberts is poised to preside over the upcoming impeachment trial against President Trump – now that House Speaker Nancy Pelosi signed a resolution Wednesday to transmit the two articles to the Senate. The Constitution requires that the vice president, in this case, Mike Pence, who normally presides over the Senate, step out in order to avoid a conflict of interest – he is next in line for the presidency if Trump is removed from office. The chief justice, therefore, is tapped to preside over an impeachment trial.

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But Roberts used the phrase Wednesday on an unrelated matter – while hearing the case of Department of Veteran Affairs employee, Norris Babb, who claims her bosses "discriminated against her based on her gender and age” and “subjected her to a hostile work environment.”

“The hiring person, who’s younger, says, ‘OK, Boomer,’ once to the applicant,” Roberts asked Babb’s attorney, Roman Martinez, suggesting a hypothetical exchange to determine when an older federal employee might be able to win a lawsuit under the Age Discrimination in Employment Act.

Wednesday was the first time, according to databases of high court arguments, the somewhat pejorative phrase used mostly by millennials and members of Gen Z after going viral on the Internet has been uttered in the Supreme Court, The Associated Press reported.

A “boomer” refers to someone from the baby boomer generation born between 1946 and 1965. Roberts, born Jan. 27, 1955, falls into this group. But justices have lifetime tenure. The nine justices on the Supreme Court range in age from 52 to 86, with Neil Gorsuch the youngest, Ruth Bader Ginsburg the eldest.

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Under federal law, employees working in the private sector or for state or local governments bear the burden of proving age prompted the discrimination. But Babb’s attorney argued that provisions in the act make it easier for government workers to sue – because they only need to prove age was one of several factors that lead to the negative action, The Washington Post reported.

“So calling somebody a ‘boomer’ and considering them for a position would be actionable?” Roberts asked, seeking clarification for the attorney’s argument.

Yes, Martinez replied, if the remark “was one of the factors going into this decision, I think it absolutely would be covered.”

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Back in November, a 25-year-old New Zealand lawmaker was accused of ageism after she responded “OK, Boomer” to an older colleague who allegedly heckled her during a debate on climate change.

Fox News' Stephen Sorace and The Associated Press contributed to this report.