A posting on Miss Pennsylvania Sheena Monnin's Facebook page claims another contestant learned the names of the top 5 finishers on Sunday morning - hours before the show was broadcast.
Monnin claims the other contestant told her the names of the top 5 she spotted on a planning sheet for the telecast - and she decided to step down as soon as those same contestants were named during the show.
"In my heart I believe in honesty, fair play, a fair opportunity, and high moral integrity, none of which in my opinion are part of this pageant system any longer," Monnin wrote in one of her Facebook posts.
Monnin, of Cranberry, Butler County, did not immediately respond to a Facebook message from The Associated Press.
Donald Trump, who runs the Miss Universe Organization, called Monnin's claims that the pageant was fixed "totally ridiculous" in a live interview Wednesday on ABC's "Good Morning America" and said the pageant organization plans to sue Monnin for making the "false charge."
"We're going to be suing her now. She made a very false charge and she knows it's a false charge," Trump said.
Pageant organizers confirmed Monnin resigned, but said it wasn't for the reason she claimed.
According to a statement from the Miss Universe Organization, the contestant who Monnin claimed saw the sheet vehemently refuted Monnin's account.
The statement includes text from an email organizers said Monnin sent citing the decision to allow transgender contestants into the competition as the reason she's resigning.
A transgender contestant was initially denied entry to the Miss Universe Canada pageant, but Trump subsequently overruled that decision.
Miss Rhode Island, the pageant's winner, Olivia Culpo, told WPRO-AM she knew Monnin "fairly well" because contestants were often positioned alphabetically by state. She said Monnin's original resignation was based on her stance on the pageant's policy on transgender contestants and called it "strange" that Monnin is now saying something else.
"It's a little iffy to me," Culpo said.
Trump downplayed the role transgender contestants had on that Monnin's decision, even though pageant claim that was her motivation.
"I don't think that she had an issue with that," Trump said. "I think her primary issue is that she lost and she's angry about losing. And frankly, in my opinion, I saw her barely a second and she didn't deserve to be in the top 15."