Rahal was cited for an incident arising from Sunday's Toyota Grand Prix of Long Beach, during which he was penalized for blocking and intentionally making contact with another driver.
Beaux Barfield, IndyCar president of competition, said the incident happened during the 22nd lap of the 85-lap race, when Rahal made contact with the No. 26 car driven by Marco Andretti.
Andretti's car briefly spun into the air before colliding with the tire barrier after the contact.
"All stewards have reviewed the incident and have decided that the on-track actions of Graham warranted probation because of driving that endangers on-track safety and adversely affects competition," Barfield said.