As UFC ends the year with its two biggest stars main eventing pay-per-views, other fighters on UFC's roster are growing upset with the company's insistence on giving Conor McGregor and Ronda Rousey title shots.

After Jose Aldo made his displeasure with Dana White and UFC known following the announcement of McGregor getting a lightweight title shot at UFC 205, it's now Julianna Pena's turn to be upset at Ronda Rousey getting a bantamweight title shot as the main event of UFC 207. Pena spoke with MMAFighting.com and noted her frustration with the "spoiled brat" Rousey getting a title shot in her return from more than a year out of the Octagon.

"It's bulls---," Peña told MMA Fighting. "That spoiled brat has gotten everything handed to her, and she's getting everything handed to her again. It's bullshit.

"I have no idea. Never in the history have I ever heard of somebody have a no-controversy brutal knockout, then quit the sport, and then comeback and get a title shot right away. The girl is mentally weak and Amanda Nunes is going to f------ knock her out and expose her ass. She's literally the worst fighter on the roster, and I can't stomach the fact that I'm not getting the title shot. I don't know how they conduct business over there, but they're going to do what they want no matter what, so there is not really much I could do. Back to the drawing board I guess."

Pena is currently ranked No. 5 on the official UFC women's bantamweight rankings despite being undefeated at 4-0 in UFC competition, most recently earning a unanimous decision victory over Cat Zingano. Rousey has not fought since suffering her first career knockout loss to Holly Holm last November.

UFC has clearly put a premium on putting its stars in main events. McGregor has been allowed to maintain the featherweight belt despite fighting three times in 2016 and not defending the belt once. Now, Rousey will get a title shot in her return to the octagon after a 13-month layoff.

Pena and Aldo's frustration is completely understandable from a fighter's point of view, but from a business perspective, UFC's decision-making also makes sense. The company's goal is to make money and no one attracts eyeballs like Rousey and McGregor. With more and more fighters like Aldo and Pena threatening to leave if things don't change, it will be interesting to see if White and UFC take a different approach in the future to giving in to the desires of the stars.