The stock closed at $9.33 on the Toronto Stock Exchange, a drop of more than nine per cent. It traded as low as $9.20, 10.3 per cent lower than Wednesday's close, earlier in the session.
Precision was the most actively traded stock on the Toronto Stock Exchange, with more than 74 million shares changing hands.
Commenting on the unusual market activity, Precision put out a brief statement explaining that AIMCo had sold its entire stake, or about 56 million shares, in an overnight transaction.
"AIMCo acted independently of Precision in both its decision to exit its position and the facilitation of the overnight marketed transaction," Precision said.
AIMCo made its investment in 2009, when Precision was struggling financially after closing a major U.S. acquisition at the onset of the recession.
The investment has paid off for AIMCo which manages $70 billion on behalf of 26 pension, endowment and government funds in Alberta.
The money manager paid $3 per unit for Precision, which was an income trust at the time.