expression, godan verb (-mu)
form a faction; band together
Often used for people grouping together for a common purpose, sometimes with a negative connotation of cliquishness or conspiracy.
彼らは徒党を組んで改革に反対した。
They banded together to oppose the reform.
徒党を組んでいじめをするのは
It is unacceptable to form a clique and bully others.