Some *NSYNC fans think all the other guys are at Justin Timberlake's beck and call these days amid these little mini collabs they've been doing... but Joey Fatone says that's BS.

We got the boy band singer at LAX on Monday and asked him all about their recent gig with JT in L.A. amid his latest album drop -- where there's a song that features *NSYNC, serving as just the latest team-up they've done in the studio ... with fans wanting the real thing.

Of course, our photog asked about the prospect of a proper reunion for *NSYNC ... and Joey gave us the standard line of not-now-but-maybe-one-day, which we've heard for months.

Basically ... Joey says everyone's busy, so there's no official coming-together happening in the near future -- but does acknowledge that if they were to get in the studio again for brand new music in 2024, it'd probably sound something very much like their new track "Paradise."

He also says that *NSYNC doesn't mind coming together for JT when they can. Although, when our camera guy asked if they're on call for Justin these days -- as some online have suggested -- he shot that notion down entirely ... saying that's not the dynamic here.

Joey tells us he understands why some might draw that conclusion -- remember, not only did *NSYNC cameo on JT's new album, but did the same for his new 'Trolls' movie too -- he assures us that the group has turned down Justin's requests before ... many times, in fact.

As our camera guy puts it ... the *NSYNC guys are NOT Justin's industry booty call -- despite what some might assume. Joey makes it very clear ... they're all booked and busy in their own respective careers, so when they collaborate ... it's only 'cause it works for everyone.