Otai levelled the charge after having one man red-carded and two yellow-carded in Saturday's 36-27 loss to Canada in Pacific Nations Cup play.
Both trips to the sin-bin — a yellow card means 10 minutes off the field for the penalized player — came from so-called shoulder charges, when a player does not use his arms in the tackle.
"I had a look at both. I couldn't really see why (the yellow cards were issued)," Otai said 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."
One of the yellow cards resulted in Canadian winger Matt Evans being carried off on a stretcher. He returned to the bench later in the match. Fullback James Pritchard needed treatment but remained on the field after the other penalized hit.
Canadian captain Aaron Carpenter said players know what to expect against Pacific Island teams.
"Sometimes they get (it) in their eyes and they see a tackle coming and they don't stop, even if you've let go of the ball," he said. "So you've just go to ride some of those."
Crowley declined to debate the merits of the Tongan play.
"It was a physical game," said the former All Black. "We've got a few boys walking around pretty wounded in there and we've got to keep an eye on a couple of them, I think."
Otai also disputed the 34th-minute red card to prop Eddie Aholelei after a melee that saw Canadian flanker Jebb Sinclair decked with a punch. Canadian fly half Nathan Hirayama and Tongan winger Fetu'u Vainikolo were lucky to stay on the pitch after trading blows early on in the incident.
Otai said Hirayama started the incident.
"It's one of those thing where we've just got to behave ourselves and let the referee do his job."