The group were in the bottom two for the third time on Sunday night, with the judges saving them ahead of Rylan Clark.
Xtra Factor host Caroline Flack admitted that the boys were "very worried" about getting the axe before the final next month in Manchester.
"It's going to be hard for them, there's only four acts left," Caroline said. "That was their third time in the bottom two, they were very worried.
"They are very pleased they got through but they're really worried they'll go this week.
Unfortunately for the group, they are the odds on favourites to fall at the final hurdle in the X Factor as we head in to the penultimate weekend of the ITV1 show.
The boy band are 10/11 with William Hill to be the next act to head home with Christopher Maloney 7/4, James Arthur 6/1 and Jahmene Douglas available at 8/1.
“Union J have impressed this series and have done very well for themselves but despite Louis Walsh claiming they are the next big boy band, they are favourites for the chop,” said William Hill spokesman Mark Young.
Jahmene Douglas and James Arthur are co 11/8 favourites for the crown with a shock Christopher Maloney win seemingly not quite so shocking at 9/2. Union J are the outsiders at 8/1.
Rylan Clark lasted eight weeks on the show and is 1/20 for an appearance ‘The Only Way is Essex’ to be his next step. A permanent job on ‘Daybreak’ or ‘This Morning’ is 2/1 with 16/1 for the Essex boy to represent the United Kingdom in the Eurovision song contest next year.
But that's what the bookies have to say, vote for your X Factor favourite in our new poll below!
The X Factor 2012 continues this weekend on ITV1 and ITV1HD with the final four acts singing songs that they hope will get them into the final.
On Sunday's results show, one more act get the axe and there will be performances from Pink and Tulisa.