The Ruderman Family Foundation, a Jewish organization that prioritizes disability rights and inclusion, called on Democratic presidential candidate Sen. Bernie Sanders (I-Vt.) to apologize for a joke directed at Republican candidates that questioned their mental health.

During Sunday’s Democratic debate in Flint, Mich., Sanders said, “You know, we are, if elected president, going to invest a lot of money into mental health. And when you watch these Republican debates, you know why we need to invest in that.”

“When millions of Americans deal with issues of mental health, it was highly inappropriate for Senator Bernie Sanders to use a real disability as a joke in last night’s Democratic presidential debate,” Jay Ruderman, president of the Ruderman Family Foundation, said Monday. “He should issue an immediate apology to Americans with mental health disabilities.”

Earlier in this election season, Republican front-runner Donald Trump was also criticized by disability rights advocates for mocking New York Times reporter Serge Kovaleski, who has a congenital joint disorder known as arthrogryposis.