Is a "clique" within a congregation a problem? If we are all brothers and sisters in Christ, doesn't this destroy the fellowship we should share in a congregation? Should this person be confronted?
Cliques within congregations do war against the unity of the family of believers. Chapters 1 and 3 of 1 Corinthians address the divisions that existed among the believers in the congregation in Corinth. That part of Scripture would be good reading material in the context of your question.
If an individual is sinning by destroying the unity of a congregation, by all means speak to that person in the spirit of Matthew 18:15-20.
Ephesians 4:3 provides good encouragement for all Christians: “Make every effort to keep the unity of the Spirit through the bond of peace.”