The boyband were criticised last week after mentor Louis Walsh had them sing 'I Swear', with the other judges branding the performance "dated".
Gary Barlow told them: "You've had a really bad night tonight. The harmonies were off. When you watch this back you'll be disappointed. I think in the battle of the boybands, Union J have taken it tonight."
They ended up in the bottom two on Sunday's results show, but were saved after the judges sent the vote to Deadlock. Melanie Masson was eliminated from The X Factor after receiving the fewest votes.
District3 told TellyMix at yesterday's rehearsal: "Louis has been doing this for years and he's got masses of experience, but this week, we've chosen our song and it's a lot more energetic than you've seen before.
"Hopefully it will go down well. Louis was happy to go with what we wanted to do this week. We don't argue or anything, it's a team."
The X Factor airs tomorrow (October 20) at 8.20pm on ITV1. This week's theme is 'Club Classics'.
Digital Spy breakfast show - watch Anna Williamson discuss the day's biggest stories including X Factor, James Bond and Justin Timberlake: