The allegation marks the latest sexual harassment charges against Spacey, who has now been accused of improper actions by more than 10 men.
Harry told Buzzfeed that his father was working on the play "Complicit" at the Old Vic with Spacey, and the two had gone to Spacey's apartment to run lines. Dreyfuss had met the actor once previous to the encounter, and described being nervous but excited when he met him for the first time.
"The first time I met him, he put all my worries to rest. He saw me and his eyes lit up. He gave me such a warm smile, and instead of shaking my hand, he gave me a hug. Instantly, my young-man-perpetually-seeking-father-figures heart melted. All I remember thinking was youre so nice," Harry said.
"After a few minutes, he put his hand on my thigh... It took that long because it just never occurred to me that Kevin would be interested in me in the first place. He was an adult man, a hero of mine, my dad's boss, none of which were categories on my radar for sexual interactions.
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"Besides, I thought, surely he can't be coming on to me like this right in front of my dad. But his hand stayed there," Harry added.
According to Harry his father did not notice the interaction because he was too engrossed with his script.
Harry again moved to a different side of the couch and, "Once again Kevin followed me, sat down, and with considerable effort, slid his hand between my right hand and my right leg. Over the course of about 20 seconds, centimeter by centimeter, Kevin crawled his hand from my thigh over toward my crotch.
"My mind went blank. Suddenly, he had completed his journey and now he had all of me in his hand. I stopped reading the script and my eyes went wide. I lifted up my head and faced him. Looking into his eyes, I gave the most meager shake of my head that I could manage."
Harry said it took him so long to come forward because for a long time, he saw his experience with sexual abuse as "relatively minor."
"A world in which powerful men are no longer allowed to feel safe to do this, or far worse. In retrospect, what disgusts me about Kevin was how safe he did feel. He knew he could fondle me in a room with my father and that I wouldn't say a word. He knew I wouldn't have had the guts. And I didn't.