This is a perfect example of how posting a single verse can be useless. Look at the context:

(Matthew 18:15-18 NIV) "If your brother sins against you, go and show him his fault, just between the two of you. If he listens to you, you have won your brother over. {16} But if he will not listen, take one or two others along, so that 'every matter may be established by the testimony of two or three witnesses.' {17} If he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, treat him as you would a pagan or a tax collector. {18} "I tell you the truth, whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven.

What it means is that someone who was disciplined by the church in one area is still bound by that discipline if they try to go to another church.