Indie and Pixie accuse coach Jessie J of favouring Becky on their performance of Beyonce track Irreplaceable.
They tell the camera: "In the splitting up of the song, it seems that she [Becky] is getting a lot of the good bits and because we're a duo, we're getting the bits that are easier to harmonise on. We look like backing singers."
The pair reveals their feelings to Jessie, saying: "We felt like we've got the safer parts of the song and we want to take risks."
But they're left annoyed when Jessie tells them it's down to the way they're singing the track rather than the way the song has been split up.
"[Jessie] kept saying don't be intimidated by Becky's big voice," the teenage pair explains. "But we do have big voices, we just don't have a chance to show it."
Jessie meanwhile admits: "If there's tension, I'm happy for that to be there, as long as it's twisted into a good performance."
And the trio's battle is one hell of a performance!
Catch it at 7:30PM on BBC One tonight!