Bone Thugs-n-Harmony -- United Against Lawsuit

The rap group Bone Thugs-n-Harmony is standing together to take on a lawsuit filed against the group stemming from an alleged altercation outside their tour bus earlier this year ... this according to one of the group's members.

As TMZ first reported, Bizzy Bone (far left) was investigated for alleged assault in Chicago back in June after two men claimed he flipped out and beat them up after they paid $80 to party with the group after a concert. According to a report, no arrests were ever made and earlier this week ... the men decided to file a lawsuit against Bizzy and the rest of the band.

Flesh-n-Bone (second from the left) tells TMZ the group feels "the truth will come out" and they plan to "deal with this in court."