I'm no expert on this subject but have delt with my own union in this regard so I'll try to help out here. In short, the answer is you are dropped from the membership rolls. The ammount of quarters you're allowed to fall behind in dues largely depends on your unions "Constitution". For mine it would be the close of the fourth quarter in arrears before I would be dropped from the rolls. Call your union on this one for more specific information, according to your unions Constitution, any agreements and supplements to that agreement.