When someone in regular attendance in a Plymouth Brethren assembly is under discipline, they are typically not permitted to partake in the Lord’s Supper. Occasionally they may be asked to leave the church. Since each assembly is autonomous and there is no denominational oversight, it’s possible for someone to be under discipline in one assembly but find a church home elsewhere. However, most assemblies are connected to one other through an informal grapevine and it’s not unusual for other assemblies to uphold the discipline determined by another assembly.
Usually, the process of church discipline follows the steps outlined in Matthew 18. If a person is repentant before the matter is brought before the elders or the entire church, they are often not put under discipline. However, if a person is considered to be living in sin, unrepentant, or showing public consequences of private sin (being pregnant out of wedlock, for example), their sin is brought before the church and it’s made known to the assembly that the person may not partake in the Lord’s Supper. If they are unrepentant and asked to leave the church, the assembly may be asked to refrain from associating with the person unless it is to try to bring them back to the Lord.
Since there is no governing authority over the assemblies, no official resources available for things like background checks and no official record of wrongs committed by assembly members, the environment is an ideal safe-haven for abusers. Particularly since it is difficult to make an accusation against an elder, particularly if his offense or abuse has been private.