The world governing body of rugby announced the probe in a two-paragraph release, saying it will not be making further comment until the investigation is complete.
Saturday's game in Kingston, Ont., saw one red card and two yellow cards given to the Tongans and one yellow card to Canada.
The Tongan red card was for a punch thrown while the two yellow cards were for shoulder charges that resulted in winger Matt Evans being stretchered off and fullback James Pritchard requiring medical attention on the field.
Otai said afterwards that Pacific Island teams were being singled out unfairly.
"I had a look at both (yellow cards). I couldn't really see why (they were issued),'' Otai told The Canadian Press in a post-game interview after reviewing tape of the incidents. "It's almost like, these days you know, when a black man is tackling harder than the other, it seems to be the way."
Asked if the Pacific Island teams were being singled out, Otai answered: "Absolutely. It's a perception a lot of times.
"And I think some of the foreigners that are involved in our team now are starting to see that. It's just hard to battle or fight that stereotype, I guess. But I'm not taking away the fact that at times we do, I guess, make mistakes in terms of tackling — if I'm talking in general. But in today's game, I couldn't justify the two yellow cards."
Asked about the comments Tuesday, Crowley pointed to three suspensions handed out by the IRB in the wake of the game.
Tongan back David Halaifonua was banned for six weeks until July 21 for a high shoulder charge on Evans, who was knocked unconscious by the hit but returned to the bench later in the game.
In rendering his decision on Halaifonua, judicial officer Alan Hudson called the incident at "the top end of the scale of seriousness for this offence."
Back Siale Piutau and prop Edmund Aholelei were each banned for three weeks.
Aholelei pleaded guilty to punching flanker Jebb Sinclair, for which he was sent off in the first half. The Tongan argued that he retaliated after seeing Sinclair head-butt a teammate in a melee. But the video apparently showed no head-butt, just the two players grappling.
Piutau was banned for three weeks to June 30 after pleading guilty to punching hooker Ray Barkwill. He argued that he threw the punch after seeing the Canadian strike a teammate in a ruck with his elbow.
Video was inconclusive on Barkwill's actions.
"The (Tongan) player's explanation that he was reacting to what he considered to be an act of foul player is unacceptable in the circumstances," Hudson ruled. "Players may not take the law into their own hands."
Asked Tuesday about the Tongan coach's comments, Crowley said the incidents were clear-cut to him.
"I don't know how you could say they were legal tackles," Crowley said of the yellow cards. "I thought the definition of a tackle was you had to use your arms for a start. It's pretty clear when you have a look at those incidents that they deserved what they got."
"You hear this story all the time," added the former All Black. "This is about the third or fourth time I've heard it, the racist sort of things. You've got to play within the laws of the game. And if you don't play within the laws of the game, you get dealt with."
The Canadian team is following the IRB concussion protocol on Evans, as a result of the Tongan hit.
Sean Duke and Sinclair are also going though the same protocol.