Spin City actor Michael J. Fox has found himself the subject of harsh criticism from conservative radio talk show host Rush Limbaugh, who calls the actor’s recent appearance in a politically-driven ad for Missouri Senate candidate Claire McCaskill “an act.”

Fox, who suffers from Parkinson’s disease, is featured in the ad supporting McCaskill’s stance on stem-cell research. During his portion of the TV ad—in which he explains how the candidate “shares his hope for cures”—Fox is seen exhibiting the shaking and stiff movements that characterize the chronic disease.

Limbaugh made his views public during his syndicated radio show Tuesday, saying that Fox was exaggerating his symptoms for the sake of the ad. “He is moving around and shaking, and it is purely an act,” Limbaugh said.

The host later retracted his statement and apologized on the air, but held fast to his belief that the actor was letting his illness be exploited. A representative for 45-year-old Fox called Limbaugh’s initial statement “appalling.” The rep tells USA Today “Anybody who understands Parkinson’s disease knows it’s because of the medicine that one experiences" involuntary behaviors similar to those exhibited by Fox in the 30-second ad.

The advertisement has since been added to the online video directory and has been accessed by one million users.

Fox was first diagnosed with the progressive central nervous system disorder in 1991 and went public with his struggle in 1998. In 2000, he stopped acting full-time because of the disease, deciding to spend more time with his wife, actress Tracy Pollan, and their four children.

He continues towork on behalf of the Michael J. Fox Foundation for Parkinson’s Research.