For the first time in nearly a decade, TLC will be reuniting for a U.S. concert tour later this year -- and TMZ has learned, the late Lisa "Left Eye" Lopes will be making a special appearance.

The group's rep tells us, Tionne "T-Boz" Watkins and Rozonda "Chilli" Thomas are currently in the planning stages of a massive 2012 reunion tour in the U.S.

So far, we're told 5 major cities have already been booked -- and even more are in the works.

But the big surprise ... we're told the group plans to pull a Tupac -- incorporating their deceased former member Left Eye in the shows, projecting her image on a big screen and working her vocals into the live performances.

FYI -- today marks 10 years since a fatal car accident in Honduras took Left Eye's life. RIP.