The amount of the fine wasn't disclosed, MLB.com reported, and because of an off-day Thursday, with Hamels beginning the suspension immediately it likely means only that his next start will be pushed back to Sunday.
Hamels admitted trying to hit Harper in the back during the first inning of the Phillies' 9-3 Sunday win over Washington, and Major League Baseball responded with a suspension.
"They're probably not gonna like me for it, but I'm not going to lie and say I wasn't trying to do it," Hamels said. "I think they understood the message and they threw it right back."
After getting aboard, Harper later came around to score on a steal of home.
The Phillies left-hander said throwing at Harper was a "welcome to the big leagues" moment for the 19-year-old phenom, who is batting .308 in his first eight games.
Hamels (4-1) earned the win with eight solid innings as the Phillies avoided a three-game sweep.