The 23-year-old McLaren driver was summoned to the stewards after the FIA reported his alleged failure to follow the race director's instructions during FP2.
Piastri finished the session in 16th around the circuit Gilles Villeneuve, as well as facing an infringement investigation.
Piastri warned by FIA
The move in question occurred at turn 14, leaving the Australian with an official warning.
Many drivers ventured off track during practice, with Piastri's team-mate Lando Norris also coming under investigation after finishing FP1 top of the table.
Thankfully for McLaren, neither Norris or Piastri received penalties for their alleged ignoring of race director's instructions.
In an official FIA statement on Piastri's alleged infringement, race officials said: “The driver of car 81 left the track at turn 14, did not touch the orange kerb on the inside and did not follow the instructions outlined in item 15 of the race director’s event notes.
“However, the stewards determine that, given the weather conditions, the driver took reasonable action not to rejoin the track in an unsafe manner and did not gain any lasting advantage and therefore consider a warning as appropriate.
“Competitors are reminded that they have the right to appeal certain decisions of the stewards, in accordance with Article 15 of the FIA International Sporting Code and Chapter 4 of the FIA Judicial and Disciplinary Rules, within the applicable time limits.”