Here's the deal ... Justin gave *NSYNC fans the ultimate tease this week when he told Kelly Clarkson he was cooking something up with the boy band, leading lotsa folks to believe new tracks and potentially a tour was coming, building on their recent reunion.

But our sources at RCA Records are pumping the brakes, telling us ... Justin's tease was referencing *NSYNC members recording background vocals for his his upcoming album, "Everything I Thought I Was."

We're told when Justin, Lance Bass, Joey Fatone, JC Chasez and Chris Kirkpatrick got together last year to record "Better Place" for 'Trolls Band Together,' they also used their time together in the studio to lay down vocals for JT's new offering.

So, JT's just hyping that collab ... background vocals for that one track, which we guess some might consider a reunion of sorts.

We're also told RCA Records honchos are adamant that when/IF *NSYNC does make a comeback, it needs to be the band's own sound and not Justin's which would also include JC singing half the leads with JT just like with all the hit *NSYNC records.

Unfortunately for *NSYNC fans, that isn't imminent ... we're told Justin is full steam ahead with his upcoming world tour and there are no plans for his old band members to join him on stage.

Of course, there's no doubt fans are clamoring for an *NSYNC reunion album and tour ... and that could become a factor in the future. Right now, our sources say RCA is concerned with Justin's first single stumbling out of the gate.

We're told RCA is nervous fans are upset they're not getting a true *NSYNC song, and that might be why Justin's "Selfish" isn't performing as well as hoped.